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B1.7
Genes
3
This lesson introduces the idea of genes and alleles, and how they are the cause of inherited variation.
Specification coverage
1.13 Describe the structure of the
nucleus of the cell as containing
chromosomes, on which genes are
located
1.14 Demonstrate an understanding
that genes exist in alternative forms
called alleles which give rise to
differences in inherited characteristics
1.11 Explain how waves will be
refracted at a boundary in terms of
the change of speed and direction
11 How and why decisions
about science and technology are
made, including those that raise
ethical issues, and about the social,
economic and environmental effects
of such decisions
The tasks in this lesson also provide
2 and 8.
opportunities to cover
Key terms
allele
cell membrane
chromosome
cytoplasm
DNA
gene
inherited variation
nucleus
B1.7a Chromosome sorting
B1.7c Chromosomes and genes
Differences
Starter 1
Lit Ask students to work in
pairs to discuss the question:
Why are we all different? If you
have a class in which there are
a number of students without
English as a first language, pair
those students with fluent English
speakers. Ask each pair to agree
on and prepare one answer to
the question. You can extend
this by asking the pairs to join
together into groups of four and
to agree on one answer.
Then ask the fours to group
together into eights to agree on
one answer.
Chromosome
sorting
Exploring 1
Worksheet 1.7a
provides a set of
human (female)
chromosomes.
Challenge students
to work out how
many pairs of chromosomes there
are in human nuclei.
Working towards A* Ask students to
work out what human chromosomes
are like.
Working towards E Tell students that
humans have 23 pairs of chromosomes
and ask them to pair up the
chromosomes.
What’s inherited?
Starter 2
Explain that inherited variation
is variation caused by your
parents. The AT presentation
What’s inherited? contains a
series of photos of different
families. Students are asked to
identify inherited characteristics
and to say which parent a
child has inherited a certain
characteristic from. This can be
done without the AT by asking
friends/colleagues to supply
family photos that you can use.
Inheritance survey
Exploring 2
Students use
Worksheet B1.7b
to conduct a
survey of inherited
characteristics that
show discontinuous
variation.
Working towards A* Ask students to
design a spreadsheet to collate their
results, calculate percentages and draw
a suitable chart or graph.
Working towards E Students use the
AT Excel spreadsheet Inheritance
survey to record their results.
Each of the cards shows a human chromosome. Cut out and sort the cards.
Sheet 1 of 1
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.
B1.7b Inheritance survey
Name
Date
___
Method
Carry out a survey to find out how these characteristics vary.
Recording your results
Total people
asked
Number
with this
Number
without this
Percentage with the
characteristic
can roll tongue
has hitchhiker’s thumb
puts left arm on top when
folding arms
has a free earlobe
has curly hair
has blue eyes
has a widow’s peak
has a dimpled chin
Considering your results/conclusions
1
a Which characteristic was the most common?
____________________________________________________________________
b Which characteristic was the least common (rarest)?
____________________________________________________________________
Evaluation
2
How could you increase the quality of your data?
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.
Cell analogies
Plenary 1 AfL
Ask groups of students to use
the idea of a car factory to
develop an analogy for cells,
chromosomes, genes and
alleles. The factory is in a
building and has a central office
that contains the instructions for
making the cars.
Chromosomes
and genes
Homework 1
Worksheet
B1.7c is
designed
for students
needing
support and
contains simple questions on
chromosomes and genes.
Working towards E Before
setting the homework, draw a
chromosome on the board
and ask students to say how
and why it should be divided
into sections.
Lego® chromosomes
Explaining 2
Make a Lego® model of a chromosome.
Make sure all the bricks are the same
size and use variations on the number
of bricks to make each ‘gene’. Explain
that the different heights of the sections
represent different genes. Show another
chromosome that is identical except that
one of the gene sections is a different
colour. Explain this is what an allele
is like – it’s the same gene but it is a
variation of that gene.
Working towards A* Students should
compare the strengths and weaknesses
of this model.
Working towards E Use only three
or four gene sections for making the
chromosomes.
SOCOs at work (AT)
Plenary 2 Demo
Show students the AT video
clip SOCOs at work. Ask them
to explain why blood is such an
important commodity in solving
crimes. This can be used as an
initiator to help students answer
the longer answer question at
the bottom of page 31. (Note
that only white blood cells
contain DNA.)
Genes and
paternity
testing
Homework 2
Worksheet
B1.7d is
designed
for students
working
at a higher level and contains
questions on chromosomes
and genes. Note that this sheet
contains a question on paternity
testing, which may be a sensitive
subject for some students.
Working towards A* Ask students
to do the ‘extra challenge’
question on the sheet.
Name
1
Class
Date
____
Most cells contain two sets of chromosomes,
which can be sorted into pairs. Some
chromosomes are bigger than others and so the
pairs can be arranged in size order. The picture
shows human chromosomes from a cheek cell.
a
b
Three of the chromosomes are missing. Draw
in the missing ones on the diagram.
Where in a cell would you find the
chromosomes?
_________________________________
c
Chromosomes are divided into ‘sections’.
Both chromosomes labelled ‘22’ contain
about 100 sections. Would you expect to find
more, less or the same number
of these sections in a chromosome like number ‘1’?
____________________________________________________________________
d
Explain your answer to part c.
____________________________________________________________________
____________________________________________________________________
e
These sections in a chromosome control characteristics. What are these sections called?
____________________________________________________________________
f
These sections have alternative forms. What are they called? Circle one word.
genes
analogues
2
alleles
nuclei
Look at the bar chart.
a
How many chromosomes does a cat have?
b
Which species has 66 chromosomes?
___________________________________
___________________________________
c
d
On the chart, fill in the missing bar for humans.
Why do you think that the total number of
chromosomes in each species is an even
number?
_______________________________
e
Do you think there is a relationship (pattern)
between the number of chromosomes and the size of the organism?
____________________________________________________________________
f
Explain your answer to part e.
____________________________________________________________________
Sheet 1 of 1
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.
B1.7d Genes and paternity testing
Class
The variations in the characteristics in table are all caused by the different alleles that different people
inherit. All the characteristics show discontinuous variation (the variations are from a fixed set of options).
You are going to find out how common these variations are.
Characteristic
Student’s Book spread B1.7
Explaining 1
Much confusion is caused by books that
show chromosomes as always being ‘X’
shaped. Chromosomes are usually in a
rod shape and only exist as ‘X’s during
cell division; the ‘X’ actually consists of
two identical lengths of DNA.
Working towards A* Challenge students
to work out the length of the central
chromosome in picture B in real life.
Working towards E Compare alleles
to types of writing implement. Each
writing implement has a different
effect when used.
Sheet 1 of 1
1
Look at the bar chart.
a
How many chromosomes does a cat have?
b
Which species has 66 chromosomes?
c
How many chromosomes are found in the body
cells of humans?
d
Why do you think that the total number of
chromosomes in each species is an even
number?
e
f
2
Do you think there is a relationship (pattern)
between the number of chromosomes and the
size of the organism?
Explain your answer to part e.
a
Where are chromosomes found in a cell?
b
What are chromosomes made of?
c The sections that chromosomes are divided into are
called genes. What do genes do?
d
3
M
C
F1
F2
What are alleles?
Sometimes there is a debate about who the father or
mother of a child is. The question can be answered by
using a DNA test. In this test, the DNA from each person
is taken and chopped into pieces. The pieces are
separated and form a pattern of bands. Each person’s
DNA produces a different pattern but there will be
similarities in the patterns for closely related people.
The diagram shows the pattern of bands from the DNA
tests on four people: a mother (M), her child (C) and two
men who could be the father (F1, F2).
a
Why are some of the bands the same in the mother
and the child?
b
Why are there differences between the DNA charts for the mother and the child?
c
Which man is most likely to be the father of the child? Explain your answer.
d
Does this prove that this man is the father? Explain your answer.
Extra challenge
4
Cells often have to make exact copies of themselves (for instance, to help you grow). So all the
chromosomes have to be copied exactly. Why is it important that the chromosomes are copied
exactly?
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.
Sheet 1 of 1
Topic B1.1: Variation
B1.7
Genes
You can think of chromosomes
as a set of books. Each book
(chromosome) contains a set of
sentences giving instructions
(genes). All of the books
together contain all of the
instructions needed to produce
a certain organism.
Where is the information for variation stored?
N
early 25 percent of all mammal species are bats!
Scientists think that bats evolved from mouse-like
animals about 50 million years ago. They think that a group
of these animals suddenly got very long ‘fingers’, which they
started to use as wings. The sudden change was caused by a
mistake in the ‘instructions’ inside cells.
Three of the main parts of most
cells are the cell membrane, the
cytoplasm and the nucleus. Inside
the nucleus there are long strands
of a substance called DNA. Each
strand forms a structure called a
chromosome.
1
2
3
4
5
6
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Alleles
Some genes for the same
characteristic (e.g. eye colour)
may contain slightly different
instructions to create variations
(e.g. brown, blue). Different forms
of the same gene are called alleles..
from two metres away.
different genes
different alleles of the same gene
E Chromosomes contain different genes, which
exist as different alleles.
chromosomes
A nucleus contains different
chromosomes. There are usually two
copies of each type of chromosome.
Chromosomes are divided up into
genes. Each chromosome carries
a large number of genes and
each gene does a particular job.
For example, many genes control
variations in our characteristics – what
we look like (e.g. eye colour, face
shape). Variation caused by genes
is inherited variation because we
inherit our genes from our parents.
40
•AT Gene intervention
[interactive]
Matching activity of definitions
with words, e.g. genetic variation:
each population has a wide range
of alleles which control their
characteristics.
•AT Artificial cell
[BBC Active Video]
Video showing the ethical debate
involved in producing an artificial cell.
Since there are two copies of every
chromosome in a body cell nucleus,
there are two copies of every gene.
Each copy of a gene may be a
different allele.
Different organisms have different
numbers of chromosomes. Human
body cell nuclei contain 23 pairs
of chromosomes, which contain
about 23 000 different genes in
total. There are many alleles for
each gene, so it is easy to see why
each of us can inherit a different set
of alleles from our parents. Each
different set of alleles gives each of
us slightly different characteristics.
In exam questions about
the differences between
the same characteristic,
write about alleles (and
not genes).
Scientists are busy
finding out what all
of our alleles do.
Imagine that an allele
is discovered that
causes a disease in
older people. Someone
suggests that all babies
are tested for this allele.
Suggest one advantage
and one disadvantage
of this testing.
4 What are alleles?
B The chromosomes in this animal cell’s nucleus are magnified x 2400.
C Human chromosomes
2 a How many
chromosomes in total
are usually found in a
human body cell?
b How many pairs are
there?
3 a Where are genes
found?
b What do genes do?
Watch Out!
chromosomes of the same type
are the same size and have the
same genes in the same order
A The heart-nosed bat can hear an insect walking
1 a Draw an animal
cell. Label the cell
membrane, cytoplasm
and nucleus.
b In which part of the
cell are chromosomes
found?
c What are
chromosomes made of?
Answers
D
Active Teach
5 Where, inside a cell, did the mistake occur that caused some mouse-like animals
to get long fingers?
6 How does the idea of alleles help us to explain why we all look different?
7 How would you add to the book analogy above to include alleles?
8 Use your knowledge of cells and genes to explain how a scientist would find out
whether blood at a crime scene belongs to the victim or to a potential suspect.
Learning
utcomes
1.13 Describe the structure of the nucleus of the cell as containing chromosomes, on which genes are located
1.14 Demonstrate an understanding that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
13 Explain how and why decisions that raise ethical issues about uses of science and technology are made
If you breed a pea that has purple flowers with one that has white flowers, what colour
will gold
the offspring
have?
Canflowers
we make
from rubbish?
41
Student book
1Drawn animal cell with correct labels
4 different versions of the same gene
to cell surface membrane, cytoplasm
5 a gene/ allele
and nucleus. b nucleus c DNA
6we all inherit the same genes but
7the matching sentences in a pair of
books are very slightly different
8blood contains cells that contain DNA
person has a different set of alleles [1]
the blood from a suspect [1]
2 a 46 b 23
since they come in many different
[1] look at DNA/alleles in the blood from
3a on chromosomes b control what
versions (alleles) we all inherit different
the crime scene [1] take sample from
Skills Spotlight
sets of alleles
the victim and look at the DNA/alleles
Advantages including living your life in a
[1] compare the two samples [1] every
way that best avoids the gene having an
characteristics are like/contain the
instructions for characteristics
effect, being prepared for the gene’s effect.
so if the DNA does not match it must be Disadvantages include being constantly
worried about the gene’s effect, employers or
insurance companies finding out and so not
employing/insuring you.
4