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CB3a.1
Modelling meiosis
Gametes are created by a form of cell division called meiosis. The three main stages of this
process are outlined below.
i
All the chromosomes in a gamete-making cell copy (replicate) their chromosomes. The copies stick to
the original chromosomes, forming X-shapes.
ii
The two sets of chromosomes split into new cells, so that each cell ends up with one copy of each type
of X-shaped chromosome.
iii
The two copies of the chromosome in each X-shape split apart into new cells.
1
Cut out the chromosomes and arrows below.
2
Use the pieces to construct a diagram to show what happens in meiosis. The organism you are modelling
has three pairs of chromosomes in its body cells. You will need to draw circles around the chromosomes to
show which cells they belong to, but you do not need to show the cell nuclei.
3
Once you are sure that your diagrams are correct, stick down the pieces on a sheet of paper.
4
Label your diagrams.
5
Explain why meiosis is needed for sexual reproduction.
6
How would this process be different in humans, compared with the model you have made?
I can…
●
describe what happens in meiosis
●
explain why haploid gametes are needed for sexual reproduction.
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1
CB3a.2
Modelling protein manufacture
1
What word describes all of the DNA in an organism’s cells?
2
What is a molecule made of repeating units called?
3
Using models can help us understand more about some processes. The assembly line in a car factory can
be used as a model of how proteins are made. When we compare something we are trying to understand
with something more familiar, we are making an analogy.
In a car factory, the central office has a number of computers in it. In the computers there are plans
that contain information about how a car is to be built and the order in which the different pieces
should be added. Information in these plans is stored in computer code.
Instructions from the computers are sent to the factory floor. The instructions are used by robots to
add pieces in the correct order, to produce a car.
Rewrite the two paragraphs above replacing the words in italics so that they explain how proteins are made
in a cell.
I can…
●
recall what an organism’s genome is
●
recall the function of genes
●
describe where genes are found.
To help you think about the model, cut out the words below and match each one to one of the words in italics in
the text above.
amino acids
amino acids
cell
chromosomes
chromosomes
chromosomes
cytoplasm
DNA
genes
genes
nucleus
protein
protein
ribosomes
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2
Gametes and genes
Strengthen
CB3a.3
Name
1
Class
Date
A zygote contains the genome of an organism.
a
What is a genome? Tick one.
all the DNA in
each cell in an
organism
b
everything inside the
cell membrane of the
cell
a description of what
an organism looks
like
all the proteins
inside the cells of an
organism
The diagram below shows a zygote being formed in an organism that has two different types of
chromosome (short and long).
What process is happening in the diagram? Tick one.
meiosis
mitosis
fertilisation
c
On the diagram, label a zygote and a gamete.
d
On the diagram, draw in the missing chromosomes.
embryology
S1 Draw a diagram to explain how a zygote’s genome is created.
2
3
4
A haploid cell contains one set of chromosomes.
a
Name one of the cells in the diagram in question 1 that is haploid.
b
How many sets of chromosomes does a diploid cell contain?
A chromosome contains a length of DNA. Certain sections of the DNA carry instructions.
a
What are these sections called?
b
What do they contain the instructions for?
a
What process makes gametes?
b
In this process, how many daughter cells does one cell produce?
c
These daughter cells are described as being 1n. What does this mean?
d
Why do the daughter cells need to be 1n?
e
By what process does a zygote grow into an embryo?
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3
Chromosomes and genes
Homework 1
CB3a.4
Name
1
Class
The table shows the number of chromosomes in the body cells of
various animals.
a
b
c
How many chromosomes are needed in a pig to contain its
entire genome?
Why are the numbers of chromosomes all even numbers?
Animal
Total number of
chromosomes in
a normal body
cell
fruit fly
4
pig
38
human
46
gypsy moth
62
dog
78
How many chromosomes would you expect to find in each of these cells?
i
ii
a human body cell
iii a gypsy moth egg cell
2
Date
a dog sperm cell
iv a pig zygote
The drawing below shows a body cell from a fruit fly.
a
Draw in its chromosomes.
b
What long molecule is found inside each chromosome?
c
Add labels for: cell surface membrane, chromosome, cytoplasm, nucleus, position of a gene.
d
What do genes contain the instructions for?
e
Unmuddle these letters to give the name of a cell part that joins amino acids together.
BRIE MOOS
f
3
In which part of the cell are these parts found?
Using some of the words from the box, complete the sentences to describe the importance of meiosis.
chromosome
haploid
daughter
male
diploid
meiosis
eight
father
mitosis
A zygote is formed when male and
mother
two
four
gametes
(2n) the gametes must be
is used to make gametes. This process produces
There are two copies of each
to
(1n).
haploid cells.
in a gamete-making cell. The two copies are slightly different.
The different copies are randomly sorted into the
produce
son
fertilisation
gametes fuse. The zygote divides by
form an embryo. To make sure the zygote is
So,
female
cells and so one gamete-making cell will
that contain different mixtures of chromosomes compared to others.
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4
Meiosis and mitosis
Homework 2
CB3a.5
1
A body cell contains a person’s genome. Define the term ‘genome’.
2
A protein is a polymer.
3
4
a
State what is meant by ‘polymer’.
b
Describe the basic structure of all proteins.
c
Where are the instructions for making a protein stored?
d
What part of a cell manufactures proteins?
Look at the diagram below. It shows two forms of cell division.
a
Explain what the diagram shows, in terms of the differences between the two processes.
b
Describe one place in which each process is used.
Explain as fully as you can why meiosis is essential in the life cycle of an organism that reproduces
sexually.
Extra challenge
5
The diagram shows the nuclei of two gamete-making cells, both from the same organism.
Copy and extend the diagram to explain how an organism makes haploid gametes that are genetically
different to one another. You do not have to draw the chromosomes exactly as they are drawn above.
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5
CB3a
Name
Progression Check
Class
Date
Progression questions
Answer these questions.
1
What happens in meiosis?
2
Why is meiosis necessary for sexual reproduction?
3
What is the role of the genome in the manufacture of proteins?
Now circle the stars in the ‘Start’ row in the table showing how confident you are of your answers – more stars
mean more confidence.
Question
1
2
3
Start



Assessment
Using a different colour, correct or add to your answers above. You may need to use the back of this sheet or
another piece of paper. Then circle the stars in the ‘Check’ row in the table – more stars mean more
confidence.
Question
1
2
3
Check



Feedback
What will you do next? Tick one box.
strengthen my learning
strengthen then extend
extend
Note down any specific areas you need to improve.
Action
You may now be given another activity. After this, note down any remaining areas you need to improve and
how you will try to improve in these areas.
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6
CB3b.1
Extracting DNA
Your teacher may watch to see if you can:
●
follow instructions carefully
●
work safely.
Aim
To extract DNA from peas.
Method
Apparatus
3
●
100 cm measuring
cylinder
●
two 250 cm
beakers
●
washing-up liquid
●
filter funnel
●
boiling tube and rack
●
ethanol (ice cold)
3
3
●
100 cm beaker
●
common salt
●
frozen peas
(thawed)
●
balance
●
water bath at 60 °C
●
clamp and stand
●
enzyme solution
●
pestle and mortar
●
filter paper
●
pipette
●
stirring rod
3
A Dissolve 3 g of salt in 100 cm of water in one of the large
3
beakers. Add 10 cm of washing-up liquid and stir in gently
until it dissolves. Do not make the mixture foamy!
B Mash 50 g of peas using the pestle and mortar. When they
are as mashed as you can make them, put them into the
other large empty beaker and add the solution you made in
step A. Stir slowly for one minute. The solution you made in
step A breaks down the cell surface membrane and the
membrane around the nucleus.
C Place the beaker in the water bath for 15 minutes.
D Using the clamp and stand (see upper diagram), pour the
mixture through a filter funnel with filter paper inside. Collect
the juice in the small beaker.
3
E
Using the measuring cylinder, measure out 10 cm of the
filtrate and pour it into the boiling tube.
F
Use a pipette to add two drops of enzyme solution. Swirl the
tube carefully and then leave it to stand in the rack for one
minute. Chromosomes also contain proteins, and the
enzymes used in this step break them down.
G Tilt the tube slightly and pour ice-cold ethanol down the side
very slowly (see lower diagram). Stop when you have added
as much ethanol as you have juice.
H Leave your tube for a few minutes. You should then see a
white layer between the juice and the ethanol. This is DNA,
and you can try to lift some of it out by winding it around a
glass stirring rod.
Considering your results/conclusions
Describe how steps B and F helped you to collect a good sample of DNA.
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7
Wear eye
protection.
Wash your hands
after the
experiment.
Keep ethanol in a
sealed plastic bag
in the freezer until
needed, with the
bottle tightly
stoppered.
CB3b.2
Name
DNA model
Class
Date
DNA consists of two helix-shaped
backbones or ‘spines’ joined together by
‘rungs’. Each rung is made of substances
called ‘bases’. Each rung contains two
bases, which are joined together. We
describe this as a ‘base pair’.
You will need a copy of the second page
of this sheet on a separate piece of paper.
A The base pairs are shown on the lefthand side. Choose four different
colours and colour in the bases, using
a different colour for each different
type of base.
B Cut out the base pairs, and colour the
backs in the same colours as their
fronts.
C Fold along the dotted lines of the base pairs.
D Cut out spines A and B.
E
Stick one of the flaps at the ends of each base pair onto one of the spines (in the rectangles shown). It does
not matter which order you put them in. You may need to hold the flaps to the spines with mini bulldog clips
or paperclips while the glue sets.
F
When the glue has set, stick the other spine onto the flaps at the other ends of the base pairs. Your model
will twist around as you stick the base pairs on. Again, you may need to hold the glued pieces together with
mini bulldog clips or paperclips while the glue sets.
G Attach a piece of string to the end of one spine (using a stapler). Hang it up to display.
1
a
Now, starting at one end of your DNA model, read off the letters of the bases that are stuck to one
spine. Write the base letters in order in the top row of boxes below. It does not matter which spine
you choose.
□□□□□□□□□□□□□□
□□□□□□□□□□□□□□
b Without looking at your model, fill in the matching bases on the bottom row of boxes.
c Check that your bottom row is correct by looking at your model.
2
3
Write down the names of the bases below.
A=
T=
C=
G=
Add labels to your model (e.g. by adding tie tags) to identify and explain these features of your model:
base, complementary base pair, hydrogen bond.
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8
CB3b.2
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DNA model
9
Looking at DNA
Strengthen
CB3b.3
Name
1
Class
Date
DNA contains four types of base: adenine, cytosine, thymine and guanine. Adenine and guanine are bigger
than cytosine and thymine. The backbones or spines of the two strands in a DNA molecule are made of
small phosphate groups and a sugar that has a pentagon shape. The diagram shows the structure.
a
Label each sugar with an ‘S’.
b
One guanine has been labelled with a ‘G’. Label all the other bases with the letters ‘A’, ‘C’, ‘G’ and ‘T’.
c
Label each phosphate group with a ‘P’.
d
Label one hydrogen bond with an ‘H’.
e
Complete this sentence to explain how the two strands in a DNA molecule are held together. All the
words you need can be found somewhere on this sheet.
The two strands of a
molecule each have a backbone of
. One of four
is attached to each sugar (A, C, T or G). The bases on
one strand are attracted to bases on the other strand – A always attracts
and
attracts
bonds. The pairs
. The attractions between the bases are called
of bases are
always
base pairs. They hold the strands of a DNA molecule together.
S1 Describe how complementary base pairs help to form the structure of DNA.
2
groups and
Explain why the structure of DNA is described as a ‘double helix’.
At the end of this topic I can…
●
recall where DNA is found in a eukaryotic cell
●
name the bases in DNA
●
describe the overall structure of DNA
●
recall the pairing of bases in DNA
●
describe how DNA strands are held together.
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10
DNA structure
Homework 1
CB3b.4
Name
1
2
3
4
Class
Date
Rearrange the letters to make the words described in the clues.
a
Where most DNA is found in a eukaryotic cell. SUN CLUE
b
A structure made of DNA packaged up with proteins. MRS MOO ECHO
c
A base found in DNA. STONY ICE
d
A molecule made of many similar units joined in a chain. ROPY ELM
Rewrite the following sentences, correcting the mistakes.
a
A DNA molecule forms a single helix.
b
DNA is made of a sugar, a nitrate group and five different sorts of bases.
c
A short length of DNA containing instructions for a protein is called a chromosome.
The diagram below shows a single strand of DNA.
a
On the diagram, fill in the letters for the complementary base pairs.
b
How are the bases joined together?
a
When scientists extract DNA from cells, they need to add chemical substances that will break down two
sets of membranes. Describe where these membranes are found.
b
To extract pure DNA, scientists add enzymes called proteases. These break down proteins. Explain
why this step is needed.
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11
The double helix
Homework 2
CB3b.5
The discovery of what DNA is made of and its structure took a
long time. Phoebus Levene (1869–1940) discovered that the four
bases in DNA (A, T, G and C) were joined to each other. A model
of his idea of the structure of DNA is shown on the right.
Erwin Chargaff (1905–2002) did further
experiments on DNA. He carefully measured
the different percentages of the four bases in
DNA from different organisms. The table shows
some of his results.
Organism
%A
%C
%G
%T
chicken
28.0
21.6
22.0
28.4
E. coli (a bacterium)
24.7
25.7
25.7
23.6
maize
26.8
23.2
22.8
27.2
human
29.3
20.0
20.7
28.4
octopus
33.2
17.6
17.6
31.6
1
How did Chargaff’s results show that Levene’s model was wrong?
2
a
Use Chargaff’s data to calculate these ratios for octopuses and humans:
i
b
3
A
C
ii
A
G
iii
A
T
iv
C
G
v
C
vi
T
G
T
In each ‘rung’ of a DNA molecule, there are two bases. There are only two options for what these bases
can be. What are those options? Explain your reasoning.
The diagram below shows part of a DNA molecule.
a
A DNA molecule is not flat like this. What shape is it?
b
Write out the sequence of letters that should be in the grey rectangles.
c
Scientists have found that it is easier to separate one pair of bases than it is the other pair. Explain this
finding.
4
When DNA is being extracted from cells, detergent is added to remove membranes. Protease enzymes
(which digest proteins) are also used. Explain why detergent and protease enzymes are needed in order to
collect pure samples of DNA.
5
State the names of the four DNA bases.
Extra challenge
6
Find out what the following people did to help finally discover the structure of DNA. Write one sentence for
each person or pair of people to summarise their contribution.
a
James Watson and Francis Crick
c
Maurice Wilkins
b
Rosalind Franklin
d
Raymond Gosling
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12
CB3b
Name
Progression Check
Class
Date
Progression questions
Answer these questions.
1
What are DNA bases?
2
What is the structure of DNA?
3
How are DNA strands held together?
Now circle the stars in the ‘Start’ row in the table showing how confident you are of your answers – more stars
mean more confidence.
Question
1
2
3
Start



Assessment
Using a different colour, correct or add to your answers above. You may need to use the back of this sheet or
another piece of paper. Then circle the stars in the ‘Check’ row in the table – more stars mean more
confidence.
Question
1
2
3
Check



Feedback
What will you do next? Tick one box.
strengthen my learning
strengthen then extend
extend
Note down any specific areas you need to improve.
Action
You may now be given another activity. After this, note down any remaining areas you need to improve and
how you will try to improve in these areas.
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purchasing institution only. This material is not copyright free.
13
Looking at alleles
Strengthen
CB3c.1
Name
1
a
Class
What is an allele? Tick one.
another word for a
chromosome
b
a type of protein
when cells have no
copies of the allele
when cells have
one copy of the
allele
when cells have two
copies of the allele
rr
rR
Rr
To produce white flowers, a pea plant needs two recessive alleles. Which of the following genotypes
will produce white flowers? Tick one.
RR
e
a colour found in
flowers
Which of the following genotypes shows two dominant alleles? Tick one.
RR
d
a version of a gene
When will a recessive allele have an effect? Tick one.
Recessive alleles
never have an
effect.
c
Date
rr
rR
Rr
Look at question S1 in the box below and then complete the genetic diagram for the cross in the
question.
S1 Two pea plants are bred together. One has two dominant alleles for purple flowers (R) and one has two
recessive alleles for white flowers (r). Draw a diagram to explain why none of the offspring will have
white flowers.
2
T is an allele that causes tall plants, and t causes short plants.
a
Which is the dominant allele?
b
Look at these genotypes: TT, Tt, tt. Which genotypes are homozygous?
c
Which genotypes in part b will cause the tall phenotype?
At the end of this topic I can…
●
describe the difference between a gene and an allele
●
describe the relationship between a genotype and a phenotype
●
identify homozygous and heterozygous genotypes
●
explain the effects of alleles on inherited characteristics
●
use genetic diagrams to work out possible combinations of alleles in the offspring of parents
●
explain why the effects of some alleles in an organism’s genotype are not seen in its phenotype.
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14
More alleles
Extend
CB3c.2
1
The gene for seed shape in pea plants has two alleles: N (smooth peas) and n (wrinkled peas).
a
Which of the alleles is dominant?
b
How do you know?
c
What is the phenotype of a heterozygous plant?
d
Why does it have this phenotype?
2
Copy the diagram and complete it to show the possible genotypes and phenotypes when both parent plants
are heterozygous for the seed shape gene.
3
A ratio shows how something is divided up. A statement like ‘there are three blues for every two reds’ is a
ratio statement. This can be written as a ratio using a colon (:) 3 : 2
What is the ratio of smooth pea to wrinkled pea phenotypes in your answer to question 2?
E1 The pea plant gene for seed shape has two alleles: N (causing smooth peas) and n (causing wrinkled
peas). Use a genetic diagram to work out the ratio of offspring plants with smooth and wrinkled peas if
the parent plants are both heterozygous.
4
a
What would you expect the phenotype ratio to be if one of the parents were homozygous for n and the
other parent were heterozygous? Show your working.
b
Pea plant X has smooth peas and has been crossed (bred) with hundreds of different pea plants. In all
these crossings, none of the offspring have ever had wrinkled peas. What is the genotype for plant X?
c
What would you expect the percentage of offspring phenotypes to be if plant X is crossed with a plant
that has wrinkled peas?
d
Two of the offspring from the cross in part c are crossed. What would you expect the different
genotypes of the offspring to be?
At the end of this topic I can…
●
describe the difference between a gene and an allele
●
describe the relationship between a genotype and a phenotype
●
identify homozygous and heterozygous genotypes
●
explain the effects of alleles on inherited characteristics
●
use genetic diagrams to work out possible combinations of alleles in the offspring of parents
●
explain why the effects of some alleles in an organism’s genotype are not seen in its phenotype.
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15
Genes and alleles
Homework 1
CB3c.3
Name
1
Class
Date
Use words from the right-hand box to complete the labelling on the diagram below. Use each word once.
alleles
chromosomes
genes
order
size
2
Look at this list of genotypes.
Mm
3
4
MM
mm
PP
Pp
pp
a
Circle the genotypes that are homozygous for the dominant allele.
b
Underline the genotypes that are heterozygous.
QQ
qq
Qq
Circle the wrong word in each sentence and write down the correct word.
a
A genotype is the proteins found in an organism.
b
The characteristics of an organism caused by alleles are its genotype.
c
A dog that is heterozygous for a dominant allele (B) that causes black fur has the genotype bB.
d
A dog that is homozygous for a dominant allele (B) will have the genotype Bb.
a
Complete the genetic diagram for this monohybrid cross between two pea plants. The allele for yellow
peas (Y) is dominant. Peas that have the recessive allele (y) have green peas.
b
Explain why none of the plants will have green peas.
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16
Genotypes and phenotypes
Homework 2
CB3c.4
1
2
3
Look at the genetic diagram below. It shows the monohybrid inheritance of a flower colour gene. The allele
B causes blue flowers and the allele b causes white flowers.
a
Copy and complete the diagram.
b
Which of the parent plants was homozygous?
c
What percentage of the offspring plants would you expect to be heterozygous?
d
What is the phenotype of parent 1?
e
What is the phenotype of parent 2?
f
Explain why there is only one phenotype in the offspring plants.
Write one sentence to describe the differences between the following pairs of words:
a
gene, allele
b
heterozygous, homozygous
c
genotype, phenotype
d
recessive, dominant.
Eating asparagus often makes people’s urine smell because sulfur compounds are excreted. The allele for
excreting sulfur compounds after eating asparagus is dominant (A). The allele for non-smelly urine is a.
Kevin’s urine does not smell after eating asparagus. His wife, Jackie, does have smelly urine. They have
five children, two of whom have non-smelly urine. Work out Jackie’s genotype for this allele.
4
Many pea plants have rounded pods, but some have flat pods because they are homozygous for a
recessive allele (d). A plant that is homozygous for the dominant allele and another plant that has flat pods
are crossed. Two of the offspring are then taken and they are crossed to produce more offspring (called F2
offspring). There are 200 F2 offspring plants. Predict the number that will have flat pods. Show all your
working.
Extra challenge
5
The phenotype for pea plant A is yellow pods and green pea coats. This plant has yellow pods because of
a recessive allele for pod colour. The coat around its peas is green because the plant is heterozygous for
the allele that causes pea coat colour.
Pea plant B is homozygous for the dominant allele for pod colour, and so has green pods. It is homozygous
for the recessive allele for pea coat colour, and so its peas have white coats.
Plants A and B are crossed. Predict the ratio of phenotypes for the offspring.
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17
CB3c
Name
Progression Check
Class
Date
Progression questions
Answer these questions.
1
What is the difference between a gene and an allele?
2
Why will a recessive allele not affect the phenotype of an organism that is heterozygous for that gene?
3
Why are genetic diagrams useful?
Now circle the stars in the ‘Start’ row in the table showing how confident you are of your answers – more stars
mean more confidence.
Question
1
2
3
Start



Assessment
Using a different colour, correct or add to your answers above. You may need to use the back of this sheet or
another piece of paper. Then circle the stars in the ‘Check’ row in the table – more stars mean more
confidence.
Question
1
2
3
Check



Feedback
What will you do next? Tick one box.
strengthen my learning
strengthen then extend
extend
Note down any specific areas you need to improve.
Action
You may now be given another activity. After this, note down any remaining areas you need to improve and
how you will try to improve in these areas.
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18
CB3d.1
A family pedigree
The cards below show members of a family. Some members of the family have a disorder caused
by a recessive allele ‘b’.
1
Cut out the cards and use the clues to construct a family pedigree chart.
2
Fill in the missing names and genotypes.
3
Shade in the circles and squares to match the phenotypes in the key.
Clues
KEY
Brian has two sons (both bb) and a daughter called Esme (BB). David and
Robert are Tracey’s sons. All three are homozygous for the normal allele.
Gavin (Bb), whose mother is June, married Tracey and they have two sons.
Kirit has a daughter with Beth, called Tara. Tara is homozygous for the
recessive allele.
Unaffected
female
Robert married Trish (Bb) and they had two sons, John and Michael. Tara’s
brothers are Yash (BB) and Grant (Bb).
Terry and June are both homozygous and have three heterozygous children –
Gavin, Beth and Brian.
Terry (BB) is Spencer’s grandfather. Brian is Spencer’s father. Tyrrell is Brian’s
partner.
BB
bb
Dabi
Male with the
disorder
Female with
the disorder
Bb
Brian
Beth
Bb
Esme
Unaffected
male
BB
bb
Kirit
BB
BB
Bb
Tara
BB
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BB
19
More genetic diagrams
Strengthen
CB3d.2
Name
1
a
Class
Diane has the genotype Kk. How many copies of the dominant allele does she have? Tick one.
none
b
one
two
three
dominant
phenotypic
k and k
neither K nor k
What is a genotype like this called? Tick one.
heterozygous
c
Date
homozygous
What alleles will Diane’s gametes contain?
K and K
K and k
d
Richard has the same genotype as Diane. Complete the
Punnett square to show the different combinations of alleles
that their children could have.
e
How many of the offspring should have a dominant allele?
f
The disorder PKU is caused by the recessive allele k. What is
the ratio of offspring without PKU to offspring with PKU?
g
What is the probability that a child of Richard and Diane’s will
not have PKU? Answer using a percentage and a decimal.
S1 Look at diagram D in CB3d Inheritance in the Student Book. Draw a Punnett square for Richard and
Diane.
S2 Work out the probability that a child of theirs will have PKU. Show all of your working.
2
The diagram on the right
shows a family pedigree
chart for a genetic disorder
caused by a recessive
allele.
a
b
c
d
In Gordon and Gwen’s
children, what is the
ratio of unaffected
children to children with
the disorder?
Which of Mark’s
grandparents is
homozygous?
What is Gordon’s
genotype?
What sex
chromosomes does
Gordon have?
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20
Peas and people
Extend
CB3d.3
Name
1
Class
Date
To answer question E1 below, a student has drawn out the diagram.
a
What is a diagram like this called?
b
Will plant A have green pods?
c
On the diagram the student has correctly given the
genotype of plant A as GG. How has the student worked
this out from question E1?
d
What is the genotype of plant B, which has yellow pods?
e
What percentage of the offspring are predicted to be Gg?
f
As a decimal, what is the predicted probability of an
offspring plant having green pods?
g
Draw a similar diagram to show what would happen if two of
those offspring were bred.
h
What is the ratio of the genotypes in this second crossing?
i
What is the ratio of the phenotypes in this second crossing?
j
What is the predicted probability of one of these offspring plants having green pods?
E1 The pea plant gene for unripe pod colour has two alleles: G (green pods) and g (yellow pods). Two
homozygous plants are crossed (bred together), one with green pods and one with yellow pods. Two of
the offspring are crossed. Work out the probability that an offspring plant from this second crossing will
have yellow pods. Show all of your working.
2
Huntingdon’s disease (HD) is caused by a dominant allele H. It causes
people to develop uncontrollable jerky movements of the body and limbs in
adulthood. Carl is heterozygous for the allele that causes HD, whereas his
wife (Gracie) is healthy. They have three children, Jack, Flora and Mark.
Their two sons both have HD; their daughter does not. Mark marries Susan
(who does not have HD). They have two children, Emma and Simon.
a
Use the symbols in the key to construct a family pedigree chart to show
this information.
b
Flora marries Adam. They have four children. What percentage of
those children would you expect to be boys? Explain your reasoning.
c
Calculate the probability that Simon has HD.
Unaffected
male
Unaffected
female
Male with HD
Female with
HD
At the end of this topic I can…
●
describe how sex is determined in humans
●
use Punnett squares to work out possible combinations of alleles in the offspring of parents
●
interpret family pedigree charts to work out possible inherited genotypes and phenotypes
●
calculate ratios of phenotypes when organisms are crossed
●
calculate probabilities of certain phenotypes occurring when organisms are crossed.
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21
Looking at inheritance
Homework 1
CB3d.4
Name
1
2
3
Class
a
Complete the Punnett square on the right to
show how sex is determined in humans.
b
What percentage of children do you expect
will be girls? Explain your answer.
c
What do the letters X and Y represent?
d
What are the names of the male and female
human gametes ?
Date
Some pea plants have yellow peas and others
have green peas. The allele for yellow (Y) is
dominant.
a
Complete the Punnett square to show the
possible combinations of alleles in the
offspring when two pea plants are crossed.
b
What is the ratio of yellow peas to green
peas in the offspring?
c
What is the probability that one of the
offspring plants will have yellow peas?
A genetic disorder called MCADD can cause people to feel sick and have fits if they do not eat for a long
period of time. The disorder is caused by a recessive allele (d). The family pedigree chart below shows how
this disorder has been passed down in one family.
a
Give the name of a male who is homozygous for the dominant allele. _________________________
b
The shading has been done correctly for the males but not for the females. On the diagram, shade in
the females who have MCADD.
c
State the genotypes of: Gary _____________ Jerry ____________ Henry __________________
d
Calculate the probability that another child of Gary and Ling’s would have MCADD. ______________
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22
Thinking about inheritance
Homework 2
CB3d.5
1
2
3
A genetic disorder called MCADD can cause people to feel sick and have fits if they do not eat for a long
period of time. The disorder is caused by a recessive allele (d). The family pedigree chart below shows how
this disorder has been passed down in one family.
a
Give the name of a male who is homozygous for the dominant allele.
b
Draw a copy of the chart. The shading has been done correctly for the males but not for the females.
On your copy of the chart, shade in the females who have MCADD.
c
What is Gary’s genotype?
d
What is Jerry’s phenotype?
e
What is Henry’s genotype?
f
Copy the Punnett square on the right and
complete it to predict the range of possible
genotypes if Gary and Ling were to have another
child.
g
What is the ratio of the different genotypes of the offspring in your Punnett square?
h
What is the ratio of the different phenotypes of the offspring in your Punnett square?
i
Calculate the probability that another child of Gary and Ling’s would have MCADD.
j
Why would none of Pepe and Sonya’s children have MCADD?
possible
gametes
Birds have Z and W sex chromosomes. The females are ZW and males are ZZ.
a
Draw a Punnett square to explain why about half of all birds that hatch are male.
b
Apart from the names of the chromosomes, how is this system different to human sex determination?
Pea plants have yellow pods or green pods. The green characteristic is dominant.
a
Draw a Punnett square for crossing a heterozygous pea plant with a homozygous recessive pea plant.
Choose your own letters for the alleles.
b
What is the probability that an offspring plant has the green pod phenotype?
Extra challenge
4
Peas (inside pea pods) can be round or wrinkled, and green or yellow. The round allele (R) is dominant and
so is yellow (Y). Work out the probability of a pea plant offspring having green, wrinkled peas if both parents
have the genotypes RrYy. You will need to draw a Punnett square with enough rows and columns to fit four
types of gamete for each parent plant.
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23
CB3d
Name
Progression Check
Class
Date
Progression questions
Answer these questions.
1
How is the sex of offspring determined in humans?
2
How do we use genetic diagrams, Punnett squares and family pedigrees to show inheritance?
3
How are the probable outcomes of offspring phenotypes calculated, using information about alleles?
Now circle the stars in the ‘Start’ row in the table showing how confident you are of your answers – more stars
mean more confidence.
Question
1
2
3
Start



Assessment
Using a different colour, correct or add to your answers above. You may need to use the back of this sheet or
another piece of paper. Then circle the stars in the ‘Check’ row in the table – more stars mean more
confidence.
Question
1
2
3
Check



Feedback
What will you do next? Tick one box.
strengthen my learning
strengthen then extend
extend
Note down any specific areas you need to improve.
Action
You may now be given another activity. After this, note down any remaining areas you need to improve and
how you will try to improve in these areas.
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24
CB3e.1
Eye colour variation
Your teacher may watch to see if you can:
●
record data suitably.
Aim
To investigate variation in human eye colour.
Prediction
1
Predict the answer to the question you are going to investigate (in step A below), and give a reason for your
answer.
Method
Apparatus
●
charts or scales for eye colour (and possibly
other characteristics, such as hair colour)
You may wish to use additional equipment. Check
with your teacher to see if it is available before
completing your planning.
A Think of a scientific question you could ask about variation in human eye colour. Discuss your idea with
others in your group and your teacher. Your teacher will have the final say on which question you will
investigate.
B Identify the information you will need to collect from each individual in order to answer your question clearly.
You may need to design a scale or a chart (e.g. for eye darkness) to compare people with.
C Draw up a tally chart to record the information you will collect.
D Collect data from as large a number of people as possible and record them in your tally chart.
Recording your results
2
Decide in which form you should display your results.
3
If needed, carry out any calculations to produce your chart or graph, e.g. totals, percentages of groups.
4
Display your results in a suitable chart or graph.
Considering your results/conclusions
5
Draw a conclusion about variation in eye colour from your results.
6
Compare your results with your prediction. Was your prediction correct? If yes, suggest why your prediction
was correct. If no, give as many reasons as you can why your prediction was wrong.
7
What produces different eye colour in different people? Explain your answer as fully as you can.
Evaluation
8
Suggest how your method could be improved to give results that are more likely to be repeatable. Explain
your suggestion.
I can…
●
give examples of characteristics controlled by multiple genes
●
explain how a mutation can cause variation.
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25
CB3e.2
Human Genome Project
The Human Genome Project (HGP) mapped the 3.3 billion base pairs in a complete human genome. The
project took over 10 years and cost over £2 billion. Since then, the mapping techniques have improved so
much that mapping a human genome takes about a day and costs about £600. This can be made even quicker
and cheaper if only small parts of the genome are mapped.
Part of the work since the HGP has been to identify genes that are related to medical issues, such as disease
and how the body responds to drugs. It is now possible to pay for a genome test that identifies the alleles that
you have for some of these genes.
Some alleles have a major effect. For example, inheriting two copies of the CF allele of the CFTR gene causes
the disease cystic fibrosis. However, having just one copy of the CF allele (the other allele being normal) will
not cause the disease.
Scientists still do not know what many of the genes identified from the HGP do. However, other research has
shown that particular alleles of particular genes seem to be linked to the risk of developing some diseases.
Alzheimer’s is a disease that usually affects older people, where changes in the brain lead to increasing
confusion and loss of memory. One of the ‘risk’ genes for Alzheimer’s is APOE, for which the most common
alleles are APOE-e2, APOE-e3 and APOE-e4. Having one APOE-e4 allele gives a ×4 increased risk of
developing the disease compared with people who do not have the allele. Having two copies increases the risk
×12. However, only about 25 per cent of the people who develop Alzheimer’s have an APOE-e4 allele, so other
factors must be involved. These other factors may include other genes or changes in the environment.
Many medical drugs are changed by enzymes once they get into the body. Depending on how the drugs were
designed, this might make them do their job better or worse. Some alleles for particular genes are linked to a
decreased effect of some drugs.
1
Explain why the Human Genome Project was important.
2
Define the following terms:
3
4
a
gene
a
Cystic fibrosis is an inherited disease. What does this mean?
b
A person who does not have cystic fibrosis has a cousin with the disease. Suggest why the person
without cystic fibrosis might have a genome test to find out whether they have the CF allele.
a
Which allele increases the risk of developing Alzheimer’s disease?
b
Explain what ‘risk’ means.
c
What is the risk of developing cystic fibrosis if a person has:
i
5
b
allele.
two CF alleles
ii
one CF allele and one normal allele?
d
Explain why having one or two APOE-e4 alleles does not mean there is a 100 per cent risk of
developing Alzheimer’s disease.
a
Describe the relationship between genes and enzymes.
b
Explain why different alleles for particular genes might affect the way drugs work in the body.
Extra challenge
6
Suggest why some people do not want to get a genome test for diseases.
7
Explain why it is important that a genome test is supported by an explanation of what the results mean.
I can…
●
describe some potential applications in medicine of mapping human genomes.
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26
Gene mutation
Strengthen
CB3e.3
Name
Class
Date
Use information in the passage below, and your knowledge, to answer the questions.
The OCA2 gene codes for the production of the protein melanin that affects the colour of eyes, skin and hair.
The gene is 344 437 bases long. Some of the bases are different in different people. Different bases affect how
much melanin is made – lots of melanin causes dark eyes, little melanin causes light (blue or grey) eyes.
A particular base at one point in the OCA2 gene is found commonly in people with dark brown eyes, but a
different base at that same point is usually found in people with blue eyes. Only a few bases in the gene seem
important in causing eye colour. Changes in bases at other points in the gene do not seem to change eye
colour.
Having a particular variation of the gene does not guarantee a particular eye colour because the OCA2 gene is
controlled by another gene called HERC2. HERC2 also has many variations. One particular variation always
causes blue eyes and pale skin, even if the bases in OCA2 code for lots of melanin.
Some variations of bases in the OCA2 gene mean no melanin is produced. This leads to albinism, where the
person has very pale hair and skin, and causes changes in the eyes that result in problems with vision. Very
pale skin is related to an increased risk of skin cancer.
1
Is eye colour controlled by a single gene or multiple genes? Give a reason for your answer.
2
What is the name for a change in a base in a gene?
3
Describe how variation in OCA2 can cause changes in eye colour.
4
Explain why variation in OCA2 does not always change eye colour.
5
Explain why variation in eye colour can be inherited.
At the end of this topic I can…
●
give examples of characteristics controlled by multiple genes
●
define the term ‘mutation’
●
describe the range of possible effects a mutation can have
●
describe some potential applications in medicine of mapping human genomes
●
explain how a mutation can cause variation
●
explain why many mutations have no effect on the phenotype.
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27
Gene mutations
Homework 1
CB3e.4
Name
1
Class
Some inherited characteristics are controlled by single genes, others are caused by multiple genes.
a
Circle the characteristic that is controlled by a single gene:
eye colour
b
2
Date
height
cystic fibrosis
skin colour
Are most human characteristics controlled by single genes or multiple genes?
The Human Genome Project was completed in 2003. Circle the letter that shows the main aim of this
project:
A to name all the human genes
B to map all the human genes that cause disease
C to map all the base pairs in one human genome
D to define what is meant by the human genome.
3
Comparing different human genomes shows that there may be differences caused by mistakes made when
the DNA is copied during cell division. What is the name for this kind of mistake in DNA?
4
Although there are differences in the DNA between different people, the people may look very similar.
Explain why.
5
The table shows some results of a genome test for one person. Clopidogrel, simvastatin and warfarin are
medicines that a doctor may give a patient to treat some diseases. Information from a genome test can help
the doctor decide how to treat a patient.
a
Which of these drugs might the doctor decide not to give the patient because it may not work well?
b
Explain your answer to part a.
c
Describe one other way that information from genomes could help in medicine.
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28
Breast cancer genes
Homework 2
CB3e.5
The techniques developed during the Human Genome Project (HGP) have helped to identify over 1800
disease-related genes. These techniques have been improved so they are now far quicker and cheaper to do
than when the project started. This has made it possible to analyse many genomes and look for variation within
the genes related to disease.
Two genes that are related to breast cancer were identified before the HGP was completed. These are the
BRCA1 and BRCA2 genes. Both genes produce proteins (BRCA1 and BRCA2 – shown in upright letters to
distinguish the protein from the gene) that normally help repair damaged DNA, particularly in breast tissue.
Damaged cells are more likely to develop into cancers than healthy cells are. This can occur in men as well as
women, although women are at greater risk as they have many more breast cells than men.
Many differences have been found in these genes between different people. Some differences are the result of
one or more changes to the DNA base pairs in the gene. Certain variations affect the risk of developing breast
cancer, as shown in the table.
Proportion of woman having
breast cancer before age 80
BRCA1
BRCA2
Bases in the relevant section of
DNA code
BRCA1
BRCA2
normal
allele
12%
12%
CAGTGTCCT
TCTATATTC
allele X
12%
12%
CAGTGCCCT
TCTATCTTC
allele Y
60–90%
45–85%
CAGAGTCCT
TCTACATTC
Women with breast cancer receive a range of treatments, often including drugs. Herceptin is a drug that targets
cancer cells that are producing a lot of the HER2 protein. These kinds of cancer cells are found in about
15–30 per cent of breast cancers. Herceptin is not only very expensive, it can also be poisonous to heart cells.
1
Describe the main aim of the Human Genome Project.
2
a
Which name is given to the process that produces a new allele of a gene?
b
When does this process usually happen?
c
Use evidence from the table to identify how alleles X and Y for each gene have changed from the
normal (most common) version.
3
Explain how the normal alleles of the BRCA1 and BRCA2 genes help to prevent the development of breast
cancer.
4
a
Explain why some variations in the BRCA genes change the risk of developing breast cancer.
b
Suggest why some variations in these genes do not change the risk of developing breast cancer.
a
Explain how a genome test could help identify the risk of developing breast cancer.
b
Explain how a genome test could help identify how breast cancer could be treated.
5
6
Allele Y shown in the table for both BRCA genes is dominant to other alleles.
a
Use a Punnett square to show the probability of inheriting a high risk of breast cancer from a father who
is heterozygous for allele Y for BRCA1 and a mother who is homozygous recessive for this gene (has
no copies of allele Y).
b
Suggest why young women in a family with a history of breast cancer might choose to have a genome
test for the BRCA genes.
Extra challenge
7
Explain how a genome test cannot identify whether a person will or will not develop breast cancer before
they are 80.
8
Suggest a reason for the values for the ‘normal’ version shown in the table above.
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29
CB3e
Name
Progression Check
Class
Date
Progression questions
Answer these questions.
1
Why is it difficult to identify how most inherited characteristics are controlled?
2
What is a mutation?
3
How can mutations cause variation?
Now circle the stars in the ‘Start’ row in the table showing how confident you are of your answers – more stars
mean more confidence.
Question
1
2
3
Start



Assessment
Using a different colour, correct or add to your answers above. You may need to use the back of this sheet or
another piece of paper. Then circle the stars in the ‘Check’ row in the table – more stars mean more
confidence.
Question
1
2
3
Check



Feedback
What will you do next? Tick one box.
strengthen my learning
strengthen then extend
extend
Note down any specific areas you need to improve.
Action
You may now be given another activity. After this, note down any remaining areas you need to improve and
how you will try to improve in these areas.
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30
CB3f.1
Variation in leaves
Introduction
Variation in living organisms may be inherited through genes or caused by differences in the environment. In
this investigation you will gather data from leaves to compare the effects of both sources of variation, and to
identify continuous and discontinuous variation. This practical will analyse class results, so it is important that
everyone uses the same method of measuring.
Your teacher may watch to see if you can:
●
measure accurately.
Aim
To investigate variation in characteristics of tree leaves.
Prediction
1
You will compare measurements of leaves from one tree. Leaves have been collected:
●
from opposite sides of a tree (e.g. north facing and south facing)
●
from outside and from inside the tree canopy.
Read the method below and then predict how each of the variables you choose to measure will vary
according to the position of the leaf on the tree. Explain your predictions.
Method
Apparatus
●
large bag (from one tree) containing four smaller bags of
five leaves (from different parts of the same tree)
●
ruler
●
callipers
●
colour chart
Wash your hands after handling
leaves.
A As a class, discuss different ways to measure the leaves, e.g. length of leaf or number of veins. For each
way, identify whether the measurements will produce continuous or discontinuous data.
B As a class, select one of the variables that is continuous and one that is discontinuous. These are the
variables you will measure. Discuss and agree a method for how these measurements will be made, e.g.
length could be the longest measurement from the point where the leaf blade joins the stalk to the tip of the
leaf, in millimetres, using a ruler.
C Take the five leaves from one of the smaller bags and record which part of the tree the leaves were
sampled from.
D Measure each leaf according to the agreed methods, and record the measurements.
E
Repeat steps C and D for each of the other smaller bags of leaves.
Recording your results
2
Record your results clearly in a table.
3
Calculate the mean for each set of measurements. Add this to your table.
4
Transfer your mean values to the class spreadsheet, making sure you identify your group and which tree
the leaves came from.
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31
CB3f.1
Variation in leaves
Considering your results/conclusions
5
Your teacher will explain how to identify anomalous results and what to do with them, and how to calculate
means for different positions of leaves on different plants.
6
Compare the mean values for your group's results with those for the whole class for the same tree.
a
How similar or different are the means?
b
Suggest a reason for any differences.
7
Which set of means and ranges (for the whole class, or just your group) do you think are closer to the real
value for the whole tree? Explain your answer, using the idea of sample size.
8
Using a suitable charting method, draw charts to show:
a
how the means for each leaf characteristic vary on the same tree
b
how the means for each leaf characteristic vary between different trees.
Remember, you will need to use different chart layouts for variables that are continuous and those that are
discontinuous.
9
a
Describe the variation in characteristics for leaves from different positions on the same tree.
b
Suggest a reason for the variation you described in a. (Hint: Think about how position of leaf relates to
the function of leaves in photosynthesis.)
10 a
b
Describe the variation in characteristics for leaves at the same position of different trees.
Give a reason for any variation in terms of genetic and/or environmental causes.
Evaluation
11 Describe any problems that you had collecting the data for this practical.
12 Explain how you could adjust the method to reduce the problems that you had.
I can…
●
distinguish between genetic variation and environmental variation
●
describe the causes of genetic variation
●
describe the causes of environmental variation
●
distinguish between continuous and discontinuous variation
●
explain how variation in a certain characteristic could be caused by genes, the environment or a
combination of both.
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32
CB3f.2
Variation in data
These charts and tables present data showing variation in organisms. Look at the data sets then answer the
questions below.
1
Decide which tables/charts show examples of the following, and explain your answers:
2
a
continuous variation
b
discontinuous variation
c
genetic variation
d
environmental variation
e
normal distribution.
For tables C and H, describe how you would present each data set in a chart. Explain your choices.
I can…
●
distinguish between genetic variation and environmental variation
●
distinguish between continuous and discontinuous variation.
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33
Variation
Strengthen
CB3f.3
S1 A child has long, wavy blonde hair, but his mother has short, straight brown hair. Give as many reasons
as you can for these differences, explaining your answers.
1
Variation is the differences in a characteristic or feature.
a
Which characteristics described in question S1 show variation?
b
One cause of genetic variation is the alleles you inherit from your parents. Which of the following
characteristics show genetic variation?
natural hair colour
dyed hair colour
wavy hair straightened by heating
c
naturally straight hair
long hair
short hair
Environmental variation is caused by differences in the environment. Suggest a change in the
environment that could cause:
i
hair colour to change from blonde to brown
ii
wavy hair to become straight
iii long hair to become short.
2
The hair colour of wild rabbits is usually brown. When two wild rabbits breed, their offspring also usually
have brown hair. Very rarely a white-haired rabbit is born. What genetic change has caused this rabbit to
have white hair instead of brown? Explain your answer.
3
Tour de France cyclists have developed very large leg muscles by exercise. Increased muscle size is an
acquired characteristic. Explain what this means.
4
The charts below show examples of variation in two different characteristics.
Chart A
Chart B
Describe the kind of variation shown in each chart, and explain your answers. Include the following terms in
your descriptions where they are useful:
continuous variation
discontinuous variation
normal distribution
At the end of this topic I can…
●
distinguish between genetic variation and environmental variation
●
describe the causes of genetic variation
●
describe the causes of environmental variation
●
distinguish between continuous and discontinuous variation
●
explain how variation in a certain characteristic could be caused by genes, the environment or a
combination of both.
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34
Variation
Homework 1
CB3f.4
Name
Class
Date
The tables show the results from two investigations into variation in human characteristics.
Table A Variation in eye colour in class 10
Table B Variation in height in boys in class 10
Natural eye colour
Frequency
(number of students)
Height group (m)
Frequency
(number of students)
blue
11
1.60–1.63
1
grey
3
1.64–1.67
3
light brown
4
1.68–1.71
6
green
1
1.72–1.75
7
dark brown
12
1.76–1.79
8
1.80–1.83
5
1.84–1.87
4
1.88–1.91
3
1.92–1.95
2
1
Is the variation shown in table A continuous or discontinuous? Explain your answer.
2
a
Draw a suitable chart on graph paper to display the data in table A.
b
Explain why you chose the type of chart you used for the data in table A.
a
Draw a suitable chart on graph paper to display the data in table B.
b
Explain why you chose the type of chart you used for the data in table B.
c
What is the modal height group for boys in class 10? Explain your answer.
3
4
The data for variation in height in table B shows a normal distribution. Explain what this means.
5
Which of the two characteristics shows variation caused only by genes? Explain your choice.
6
The other characteristic is caused by differences in genes and differences in the environment. Suggest a
reason for the variation due to the environment.
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35
Twin studies
Homework 2
CB3f.5
Many human characteristics are affected both by genes and by the environment. This includes characteristics
relating to health and to behaviour. Twin studies have been used to help identify how much of the variation
between individuals for some of these characteristics is caused by genes.
Twin studies compare identical and fraternal twins. Identical twins occur when a fertilised egg divides
completely in two soon after fertilisation. Fraternal twins are produced when two eggs are released at the same
time and each is fertilised by a different sperm. The average number of alleles that fraternal twins share is 50
per cent.
1
Give one example of a characteristic that shows variation due to genes, one that varies due to the
environment, and one that varies due to genes and the environment. Explain each of your choices.
2
What proportion of alleles do identical twins have in common? Explain your answer.
3
Explain why the value of 50 per cent for fraternal twins is an average.
4
If a characteristic is caused by genes only, and one twin has a particular variation of that characteristic,
what is the probability that their twin also has it if they are:
5
a
fraternal twins
b
identical twins?
a
If variation is caused by the environment only, which of these would twin studies most likely show:
i
more identical twins than fraternal twins have the same variation in the characteristic
ii
fewer identical twins than fraternal twins have the same variation in the characteristic
iii a similar proportion of identical and fraternal twins have the same variation.
b
6
Explain your answer to part a.
The chart shows the results from twin studies for some characteristics.
Concordance between twins with certain conditions. A concordance of 1.0 means that if one twin has the
condition, the other twin always has it. A concordance of 0.0 means that if one twin has the condition, the other
twin never has it. MZ = identical twins; DZ = non-identical twins. The number in each bar is the number of pairs
of twins in that study group.
a
Which characteristic shows variation that is most affected by genes? Explain your choice.
b
Which characteristic shows variation that is most affected by the environment? Explain your choice.
Extra challenge
7
The differences between identical twins increase with age. How can this be explained by genes?
8
Use the values in the bars to decide which results you can be most sure of. Explain your answer.
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36
CB3f
Name
Progression Check
Class
Date
Progression questions
Answer these questions.
1
How is genetic variation caused?
2
How can the environment affect characteristics?
3
What are discontinuous and continuous variation?
Now circle the stars in the ‘Start’ row in the table showing how confident you are of your answers – more stars
mean more confidence.
Question
1
2
3
Start



Assessment
Using a different colour, correct or add to your answers above. You may need to use the back of this sheet or
another piece of paper. Then circle the stars in the ‘Check’ row in the table – more stars mean more
confidence.
Question
1
2
3
Check



Feedback
What will you do next? Tick one box.
strengthen my learning
strengthen then extend
extend
Note down any specific areas you need to improve.
Action
You may now be given another activity. After this, note down any remaining areas you need to improve and
how you will try to improve in these areas.
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37
CB3
Word Sheet
CB3a – Meiosis
Word
Pronunciation
Meaning
chromosome
krow-mO-sOwm
A structure found in the nuclei of cells. Each
chromosome contains one enormously long DNA
molecule packed up with proteins.
daughter cell
dor-ter sell
A cell produced by another cell that has divided.
diploid
dipp-loyd
A cell or nucleus that has two sets of chromosomes.
In humans, almost all cells except the sperm and egg
cells are diploid.
DNA
Deoxyribonucleic acid. A polymer made of sugar and
phosphate groups joined to bases. One molecule of
DNA is found in each chromosome.
egg cell
The female gamete in humans.
fertilisation
fert-ill-I-zay-shun
Fusing of a male gamete with a female gamete.
gamete
gam-meet
A haploid cell used for sexual reproduction.
gene
jeen
Section of the long strand of DNA found in a
chromosome, which often contains instructions for a
protein.
genome
jee-nOhm
All the DNA in an organism. Each body cell contains
a copy of the genome.
haploid
happ-loyd
A cell or nucleus that has one set of chromosomes.
Gametes are haploid.
meiosis
my-O-sis
A form of cell division in which one parent cell
produces four haploid daughter cells.
mitosis
my-tO-sis
A form of cell division in which one parent cell
produces two diploid daughter cells.
polymer
poll-ee-mer
A molecule made out of a chain of repeating similar
units (called monomers).
replicate
When DNA replicates it makes a copy of itself.
sperm cell
The male gamete in humans.
zygote
zY-goat
Another term for ‘fertilised egg cell’.
Word
Pronunciation
Meaning
adenine
add-en-een
One of four bases found in DNA. Often written as A.
CB3b – DNA
base (in DNA)
chromosome
Four substances that help make up DNA, often
shown by the letters A, C, G and T. Pairs of bases
form ‘links’ between two ‘spines’ formed of phosphate
groups and a type of sugar.
krow-mO-sOwm
complementary base
pair
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A structure found in the nuclei of cells. Each
chromosome contains one enormously long DNA
molecule packed up with proteins.
Two DNA bases that fit into each other and link by
hydrogen bonds. There are two types of
complementary base pair: A linking with T, and C
linking with G.
38
CB3
Word Sheet
Word
Pronunciation
Meaning
cytosine
cY-tO-seen
One of four bases found in DNA. Often written as C.
DNA
Deoxyribonucleic acid. A polymer made of sugar and
phosphate groups joined to bases. One molecule of
DNA is found in each chromosome.
double helix
Two helices joined together.
gene
jeen
Section of the long strand of DNA found in a
chromosome, which often contains instructions for a
protein.
guanine
gua-neen
One of four bases found in DNA. Often written as G.
hydrogen bond
thymine
Weak force of attraction caused by differences in the
electrical charge on different parts of different
molecules.
thY-meen
One of four bases found in DNA. Often written as T.
Word
Pronunciation
Meaning
allele
a-leel
Most genes come in different versions, called alleles.
So a gene for eye colour may have a version (allele)
that can cause dark eyes and an allele that can
cause pale eyes.
CB3c – Alleles
dominant
Allele that will always affect the phenotype (as
opposed to a recessive allele, whose effect will not
be seen if a dominant allele is present).
genetic diagram
Diagram showing how the alleles in two parents may
form different combinations in the offspring when the
parents reproduce.
genetic variation
Also called inherited variation. Differences between
organisms passed on to offspring by their parents in
reproduction.
genotype
jee-nO-tYpe
The alleles for a certain characteristic that are found
in an organism. Written in a shorthand using letters to
represent the alleles (with the dominant allele having
a capital and being written first).
heterozygous
When both the alleles for a gene are different in an
organism.
homozygous
When both the alleles for a gene are the same in an
organism.
monohybrid
inheritance
mon-O-hy-brid in-herr-itanse
The study of how the alleles of just one gene are
passed from parents to offspring.
phenotype
fee-nO-tYpe
The characteristics that a certain set of alleles
produce.
ratio
ray-shee-O
A relationship between two quantities, usually
showing the number of times one value is bigger than
the other. For example, if there are six red buttons
and two blue buttons, the ratio of red to blue is 3 to 1,
also written 3:1.
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39
CB3
Word Sheet
Word
Pronunciation
Meaning
recessive
res-ess-iv
Allele that will only affect the phenotype if the other
allele is also recessive. It has no effect if the other
allele is dominant.
zygote
zY-goat
Another term for ‘fertilised egg cell’.
CB3d – Inheritance
Word
Pronunciation
Meaning
family pedigree chart
A chart showing the phenotypes and sexes of several
generations of the same family, to track how
characteristics have been inherited.
probability
The likelihood of an event happening. Can be shown
as a fraction from 0 to 1, a decimal from 0 to 1 or as
a percentage from 0% to 100%.
Punnett square
Diagram used to predict the different characteristics
in the offspring of two organisms with known
combinations of alleles. You can use the square to
work out the probability (how likely it is) that offspring
will inherit a certain feature.
sex chromosome
krow-mO-sOwm
Chromosome that determines the sex of an
organism. In humans, males have one X sex
chromosome and one Y sex chromosome, while
females have two Xs.
CB3e – Gene mutation
Word
Pronunciation
Meaning
Human Genome
Project
jee-nOhm
The project that mapped the base pairs in one
human genome.
mutation
mew-tay-shun
A change to a gene, caused by a mistake in copying
the DNA base pairs during cell division or by the
effects of radiation or certain chemicals.
variation
vair-ee-ay-shun
Differences in the characteristics of organisms.
Word
Pronunciation
Meaning
acquired
characteristic
ak-wired
A characteristic that can change during life, due to a
change in the environment. (See also environmental
variation.)
CB3f – Variation
continuous variation
Continuous data can take any value between two
limits. Examples include length, mass, time.
Continuous variation is when differences in a
characteristic are continuous.
discontinuous
variation
Data values that can only have one of a set number
of options are discontinuous. Examples include shoe
sizes and blood groups. Discontinuous variation is
when differences in a characteristic are
discontinuous.
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40
CB3
Word
Pronunciation
Word Sheet
Meaning
environmental
variation
Differences between organisms caused by
environmental factors, such as amount of heat, light,
damage. These differences are called acquired
characteristics.
genetic variation
Differences between organisms caused by
differences in the alleles they inherit from their
parents, or differences in genes caused by mutation.
mean
An average calculated by adding up the values of a
set of measurements and dividing by the number of
measurements in the set.
median
The middle value in a data set.
mode
The most common value in a data set.
normal distribution
When many individuals have a middle value for a
feature, with fewer individuals having greater or
lesser values. This sort of data forms a bell shape on
charts and graphs.
range
The difference between the highest and lowest
values in a set of data (usually ignoring any outliers
or anomalous results).
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41