Download Cell division and inheritance

Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
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Biology workbook
Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
WORKBOOK 7 – CELL DIVISION & INHERITANCE
Characteristics are passed on from one generation to the next in both plants and animals.
Simple genetic diagrams can be used to show this. There are ethical considerations in
treating genetic disorders.
Candidates should use their skills, knowledge and understanding to:
■ explain why Mendel proposed the idea of separately inherited factors and why the
importance of this discovery was not recognised until after his death
■ interpret genetic diagrams, including family trees
■ construct genetic diagrams of monohybrid crosses and predict the outcomes of
monohybrid crosses and be able to use the terms homozygous, heterozygous,
phenotype and genotype
■ predict and /or explain the outcome of crosses between individuals for each possible
combination of dominant and recessive alleles of the same gene
■ make informed judgements about the social and ethical issues concerning the use of
stem cells from embryos in medical research and treatments
■ make informed judgements about the economic, social and ethical issues concerning
embryo screening.
Additional guidance:
Candidates should be familiar with the principles Mendel used in investigating
monohybrid inheritance in peas. They should understand that Mendel’s work preceded
the work by other scientists which linked Mendel’s ‘inherited factors’ with chromosomes.
Additional guidance: HT only
Foundation Tier candidates should be able to interpret genetic diagrams of monohybrid
inheritance and sex inheritance but will not be expected to construct genetic diagrams or
use the terms homozygous, heterozygous, phenotype or genotype.
Subject Content: Cell division
a) In body cells the chromosomes are normally found in pairs. Body cells divide by
mitosis.
b) The chromosomes contain the genetic information.
c) When a body cell divides by mitosis:
■ copies of the genetic material are made
■ then the cell divides once to form two genetically identical body cells.
d) Mitosis occurs during growth or to produce replacement cells.
e) Body cells have two sets of chromosomes; sex cells (gametes) have only one set.
f) Cells in reproductive organs – testes and ovaries in humans – divide to form gametes.
g) The type of cell division in which a cell divides to form gametes is called meiosis.
h) When a cell divides to form gametes:
■ copies of the genetic information are made
■ then the cell divides twice to form four gametes, each with a single set of
chromosomes.
i) When gametes join at fertilisation, a single body cell with new pairs of chromosomes is
formed. A new individual then develops by this cell repeatedly dividing by mitosis.
Additional guidance:
Knowledge and understanding of the stages in mitosis and meiosis is not required.
Candidates should develop an understanding of the relationship from the molecular level
upwards between genes, chromosomes, nuclei and cells and relate these to tissues,
organs and systems.
For Foundation Tier, knowledge of meiosis is restricted to where the process occurs and
that gametes are produced by meiosis.
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
Subject content – cell differentiation & stem cells
j) Most types of animal cells differentiate at an early stage whereas many plant cells
retain the ability to differentiate throughout life. In mature animals, cell division is mainly
restricted to repair and replacement.
k) Cells from human embryos and adult bone marrow, called stem cells, can be made to
differentiate into many different types of cells, eg nerve cells.
l) Human stem cells have the ability to develop into any kind of human cell.
m) Treatment with stem cells may be able to help conditions such as paralysis.
n) The cells of the offspring produced by asexual reproduction are produced by mitosis
from the parental cells. They contain the same alleles as the parents.
Subject Content - Genetic variation
a) Sexual reproduction gives rise to variation because, when gametes fuse, one of each
pair of alleles comes from each parent.
b) In human body cells, one of the 23 pairs of chromosomes carries the genes that
determine sex. In females the sex chromosomes are the same (XX); in males the sex
chromosomes are different (XY).
c) Some characteristics are controlled by a single gene. Each gene may have different
forms called alleles.
d) An allele that controls the development of a characteristic when it is present on only
one of the chromosomes is a dominant allele.
e) An allele that controls the development of characteristics only if the dominant allele is
not present is a recessive allele.
f) Chromosomes are made up of large molecules of DNA (deoxyribo nucleic acid) which
has a double helix structure.
g) A gene is a small section of DNA.
h) Each gene codes for a particular combination of amino acids which makes a specific
protein.
i) Each person (apart from identical twins) has unique DNA. This can be used to identify
individuals in a process known as DNA fingerprinting.
Additional guidance:
Knowledge and understanding of stem cell techniques is not required.
Candidates are not expected to know the names of the four bases or how complementary
pairs of bases enable DNA replication to take place.
HT only - Candidates should understand that genetic diagrams are biological models
which can be used to predict the outcomes of crosses.
Subject content - Genetic disorders
a) Some disorders are inherited.
b) Polydactyly – having extra fingers or toes – is caused by a dominant allele of a gene
and can therefore be passed on by only one parent who has the disorder.
c) Cystic fibrosis (a disorder of cell membranes) must be inherited from both parents. The
parents may be carriers of the disorder without actually having the disorder themselves. It
is caused by a recessive allele of a gene and can therefore be passed on by parents,
neither of whom has the disorder.
d) Embryos can be screened for the alleles that cause these and other genetic disorders.
Additional guidance:
Knowledge and understanding of genetic fingerprinting techniques is not required.
Attention is drawn to the potential sensitivity needed in teaching about inherited
disorders.
Knowledge and understanding of embryo screening techniques is not required.
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Wellsway school science dept.
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Curriculum 2011 – AQA Additional Science
Biology workbook
Structures in the nucleus.
Discuss with your teacher the role of the nucleus and how the nucleus, chromosomes,
genes and DNA are all linked.
Using labelled diagrams show this relationship in the space below:
If you have finished….. Find out how DNA’s coded information affects an organism’s
inherited characteristics:
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Curriculum 2011 – AQA Additional Science
Biology workbook
DNA
1. (Optional practical.)
Using the method provided, prepare some DNA from Kiwi Fruit or Onion.
2. Write down 2 reasons why we might we need to extract DNA from cells.
a.
b.
3. An interesting calculation!
Calculate how many times to the moon and back a human’s DNA would reach if it was
removed from each cell and each strand was laid end to end. Each cell nucleus in a
human holds about 2 metres of DNA. A typical adult is comprised of approx. 50 trillion
cells (A trillion is 1 000 000 000 000). The distance from the Earth to the moon is 380000
kilometres.
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Genetic Fingerprinting
Discuss Genetic fingerprinting with your teacher.
The DNA in your cells is as unique as your fingerprints. Unless you have an identical
twin your ‘genetic fingerprint’ is different from anyone else’s
1. Complete the following paragraph:
DNA can be analysed by genetic f___________________________. This involves
c_____________ the DNA into short p___________ and then separating them into
bands. The p____________________ of the bands can then be c_________________
to show s_____________________ and differences in the DNA.
WORD LIST:
Cutting
compared
fingerprinting
patterns
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pieces
similarities
Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
2. Look at the genetic fingerprints below.
The fingerprints labelled 1-7 are suspects in a murder investigation. The fingerprint in the
middle of the picture was DNA found at the scene of the crime.
Answer the questions below:
a. Who do you think committed the murder?
b. Explain your answer clearly:
3. Go to the following website:
http://library.thinkquest.org/C0125833/english/whodunit.php
In the interactive menu option complete the “Whodunit”? scenario (DNA fingerprint game)
The 3 suspects are Jason Chua, Melvin Tan and Danny Lee.
a. Write down who was most likely to have committed the crime & explain your answer:
b. Why can you not be certain that your suspect committed the crime?
4. Read P292 ‘Biology For You’ and write down who you think is the guilty suspect.
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Cell Division – Mitosis
Watch the video or PowerPoint presentation on Mitosis & answer the questions below:
1. Write down the three reasons why it is so important that cells must divide.
a.
b.
c.
2. How many sets of chromosomes are present in normal body cells? Where does each
set originate from?
3. How many “daughter” cells are formed from each cell which divides by mitosis?
4. How does the number of chromosomes and genetic information in each daughter cell
compare with that in the parent cell?
5. What is the modern term for the production of identical offspring by mitosis?
6. Draw a diagram showing the production of 2 daughter cells from one parent cell:
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Curriculum 2011 – AQA Additional Science
Biology workbook
Cell Division – Meiosis
Watch the video or PowerPoint presentation on Meiosis & answer the questions below:
1. What is the purpose of meiosis?
2. What is the purpose of gametes (sex cells)?
3. Where does meiosis take place?
4. TRUE or FALSE: meiosis takes place in egg and sperm cells.
(If the answer is false, write out a correct statement about egg and sperm):
5. How many sets of chromosomes are present in the cells which produce gametes?
6. How many sets of chromosomes are present in gametes? Why is this important?
7. How many times does a cell divide during meiosis to produce a gamete?
8. How many “daughter” cells are formed from each cell which divides by meiosis?
9. How does the number of chromosomes and genetic information in each daughter cell
compare with that in the parent cell?
6. Draw a diagram showing the production of 4 daughter cells from one parent cell:
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Cell differentiation & stem cells
Read your textbook or support material on growth in animals and plants.
1. Describe the main differences between growth in animals and plants in terms of:
a. where growth takes place.
b. how long animals and plants can keep growing.
c. ability of tissues and organs to regenerate from undifferentiated cells.
d. which regions of plants and animals retain the ability to divide by mitosis.
2. a. Find out what stem cells are. Use your textbook, support materials, or an internet
search.
b. Explain how stem cells can be used to treat certain disorders, e.g. paralysis.
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Curriculum 2011 – AQA Additional Science
Biology workbook
c. Discuss the advantages and possible ethical problems of using stem cells, especially
those from human embryos, to replace damaged tissues.
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Boy or Girl
Chromosomes are usually found in pairs in the nucleus of each body cell. These are
called homologous pairs.
Humans have 23 pairs (46) of chromosomes. Different species of plants and animals
have different numbers of chromosomes e.g. cats have 19 pairs. In all mammals, males
have one X and one Y chromosome, but females have two X chromosomes.
The pictures (A and B) below show matched sets of chromosomes in the male and
female of an organism.
A
B
a. What species of mammal have these 2 pictures come from? Explain your answer:
b. Which one is male and which is female? Explain your answer:
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Curriculum 2011 – AQA Additional Science
Biology workbook
Discuss with your teacher how the sex chromosomes can determine the sex of an
individual.
Think about which chromosomes, X or Y can be carried by the egg and sperm
(remember – a gamete can only carry ONE of a pair of chromosomes).
Your teacher will explain to you about how to draw and use a PUNNETT SQUARE.
c. Complete the diagram to show the probability of a couple having a boy or girl baby:
PARENT:
Male
Female
SEX CHROMOSOMES: (2)
SEX CHROMOSOME
IN GAMETES:
(1)
or
PUNNETT SQUARE:
CHROMOSOME IN
GAMETES
Probability of a boy baby:
Probability of a girl baby:
d. The sex (gender) of a baby is ultimately determined by the type of sex chromosome
the sperm carries. Explain why.
e. Henry VIII either divorced or beheaded wives who were unable to give him a boy child.
Was Henry correct in his assumption that his wives had failed him? Explain your answer
clearly:
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Genetics crosses
a. Gregor Mendel
Read the passage below and answer the questions:
Gregor Mendel was an Austrian monk born in 1822. His work on pea plants in 1865
marked the start of modern genetics. He investigated the height of pea plants which
were all either tall or dwarf.
He started off by taking plants which was pure-breeding for tallness( this means when
bred with itself or other tall plants they only produced tall plants)and plants which were
pure-breeding for dwarfness (this means when bred with itself or others dwarf plants they
only produced dwarf plants). He then cross-fertilized these two plants by taking pollen
from each one.
To Mendel’s surprise he found that all the plants produced from the cross were tall. He
concluded that “When pure breeding plants with contrasting traits (e.g. tall and dwarf) are
crossed, all the offspring will resemble one parent”.
He then crossed several of these tall plants which he had produced. Again to his
surprise he found there was a 3:1 ratio of tall to dwarf plants. He concluded that ‘for
every characteristic each individual must have two determiners or factors (now known as
genes).
a. What did Mendel investigate?
b. What are pure breeding plants?
c. When Mendel cross-pollinated pure breeding tall and dwarf plants what did he find?
d. When he cross-pollinated these tall plants which he had produced, what did he find?
e. What did he conclude (find out) from this?
f. What are these determiners or factors now known as?
g. Find out why Mendel’s ideas were not recognised / accepted until 1900.
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
b. Key terminology
There are quite a few new words to learn in genetics. Discuss with your teacher &
research what the following terms mean, then write down a short definition below:
Genotype
Phenotype
Allele
Dominant
Recessive
Homozygous
Heterozygous
In genetics we use capital letters for dominant alleles and lower case for recessive alleles
Complete the following table. The first one has been done for you
Allele name
& letter
Homozygous
dominant
genotype
Tongue rolling
Can roll = T
Can’t roll = t
Eye colour
Brown = B
Blue = b
Ear lobes
Free
=E
Attached = e
TT
phenotype
(can roll)
Heterozygous
genotyp
e
Tt
phenotype
(can roll)
Homozygous
recessive
genotype
tt
phenotype
(can’t roll)
(brown eyes)
(brown eyes)
(blue eyes)
(free lobes)
(free lobes)
(attached
Lobes)
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
c. Monohybrid Inheritance
When a characteristic is determined by just one pair of alleles we can do a simple
genetics cross to investigate the mechanism of inheritance. This is called Monohybrid
Inheritance.
With the help of your teacher complete the following crosses involving eye colour:
i. 2 Homozygous parents, one with brown eyes, one with blue eyes.
Parents’ phenotype:
brown eyes
Parents’ genotype:
BB
Parents’ gametes:
(egg and sperm)
B
or
blue eyes
bb
B
b
or
b
Offspring genotypes:
All the offspring have _______________ eyes
ii. 2 Heterozygous parents, both with brown eyes.
Parents’ phenotype:
brown eyes
brown eyes
Parents’ genotype:
Parents’ gametes:
(egg and sperm)
or
Offspring genotypes:
(Draw a Punnett square)
The genetics diagram shows a _____:______ ratio of brown to blue eyes.
This is called the MONOHYBRID RATIO
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Curriculum 2011 – AQA Additional Science
Biology workbook
iii. A heterozygous brown eyed parent and a blue eyed parent.
Parents’ phenotype:
brown eyes
blue eyes
or
or
Parents’ genotype:
Parents’ gametes:
(egg and sperm)
Offspring genotypes:
(Draw a Punnett square)
The diagram shows a _________:_________ ratio of __________ to __________ eyes.
Genetics Practice Questions.
The questions below get increasingly more difficult, have a go!
Answer on separate paper
1. The coat colour of mice is controlled by a single gene. This gene has 2 alleles B and b.
a. A mouse with black fur (genotype BB) was crossed with a mouse with white fur
(genotype bb). All the baby mice were black. Use a genetics diagram to explain why all
the mice had black fur.
b. A different mouse with black fur (Bb) was crossed with a mouse with white fur (bb).
Use a genetics diagram to explain why some of the baby mice had black fur and some
had white fur.
2 .Draw genetics diagrams to predict the possible outcome when two heterozygous
tongue rolling people (Tt) have children. The tongue rolling allele is dominant to the nonrolling allele.
3. A homozygous long haired cat is crossed with a homozygous short haired cat and
produces a litter of 9 long haired kittens. Show the probable offspring which would be
produced if two of these kittens were mated, including genotype and phenotype ratios.
4. In humans, the allele for wavy hair is dominant to that for straight hair. (In your answer
use H to represent the allele for wavy hair and h to represent the allele for straight hair)
a. Explain the meaning of this statement:
“A person with wavy hair may be heterozygous or homozygous for this characteristic”.
b. Explain why a man with straight hair married to a woman with straight hair is unlikely to
have any children with wavy hair.
c. By means of a genetic diagram explain why a man with wavy hair who marries a
woman with wavy hair may have some children with straight hair.
5. Can you draw the genetics diagrams for Mendel’s experiment with pea plants?
Use T to represent the allele for tallness and t to represent the allele for dwarfness.
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Curriculum 2011 – AQA Additional Science
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Genetic disorders
Discuss Genetic Disorders with your teacher.
Watch the PowerPoint or read your textbook on Genetic Disorders.
a. What is a Genetic Disorder?
b. What is a mutation?
c. Write down the name of 3 examples of Genetic Disorders.
The chance of children inheriting a genetic disorder from its parents depends on 2 things:
i. Whether one or both parents have one or more alleles for the genetic disorder;
ii. Whether the genetic disorder is caused by a dominant or recessive allele.
d. In the disorder POLYDACTYLY, people have more fingers or toes than usual.
The disorder is caused by a dominant allele, P.
In the space below, carry out a genetics cross as indicated and find out the probability of
children inheriting the disorder:
i. A heterozygous man for Polydactyly has children with a normal-fingered woman.
Parents’ phenotype:
Polydactyl man
Normal woman
or
or
Parents’ genotype:
Parents’ gametes:
(egg and sperm)
Offspring genotypes:
(Draw a Punnett square)
The diagram shows a _________:_________ ratio of Polydactyl and normal children.
ii. How would the ratio of polydactyl to normal children differ if both parents were
heterozygous for Polydactyly?
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Curriculum 2011 – AQA Additional Science
Biology workbook
e. Cystic Fibrosis
Discuss Cystic Fibrosis with your teacher.
Watch video clips which show cystic fibrosis (CF) or read your textbook.
Answer the questions below:
i. Describe the main symptoms of CF.
ii. What kind of allele causes CF?
iii. People who are heterozygous for CF are described as SYMPTOMLESS CARRIERS.
Explain what this means, & why they have no symptoms of CF.
iv. Can 2 normal people or one normal person and one symptomless carrier have
children with CF? Explain your answer in each case.
v. Can 2 symptomless carriers have children with CF?
Complete a genetic cross & calculate the % probability that a child will be born with CF.
(Label the dominant normal allele N and the recessive CF allele n)
Parents’ phenotype:
male symptomless
carrier
female symptomless
carrier
Parents’ genotype:
Parents’ gametes:
or
or
Offspring genotypes:
(Draw a Punnett square)
The diagram shows a _________:_________ ratio of normal & symptomless carriers to
CF children.
vi. Embryo screening can be used to test for defective alleles including the CF allele.
Explain what is meant by embryo screening.
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Curriculum 2011 – AQA Additional Science
Biology workbook
vii. (If you have finished…. )
Approximately 1 in 25 people are symptomless carriers of CF. What is the likely
incidence of CF in the population? Show your working.
Well done! You have now completed the Cell division & Inheritance topic.
Useful web links:
The student room
http://www.thestudentroom.co.uk/wiki/Revision:GCSE_Biology_-_Genetics__Variation,_Mitosis_and_Meiosis#Mitosis
s-cool
http://www.s-cool.co.uk/gcse/biology/genes-and-genetics
revision world
http://www.revisionworld.co.uk/gcse/biology/genetics-and-dna
bbc bitesize
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/celldivision/inheritance1.shtml
gcse-genetics
http://twig-it.com/gcse-genetics
purchon
http://www.purchon.com/biology/genetics.htm
biology resources
http://www.biology-resources.com/biology-questions.html
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Glossary (muddled – sort them out!)
Allele
Contains the genetic code, Shaped like a double helix
Chromosome Controls your characteristics. It is a section of DNA molecule
DNA
Found in the cell nucleus, X shaped, contains many genes.
Dominant
The alternative form of a gene e.g. Alleles for eye colour brown and
blue
Gene
Controls the development of a characteristic even when it is present on
only one of the chromosomes in a pair
Genetics
Paired chromosomes; only come together at the start of meiosis
Genotype
The chromosomes in a pair contain different alleles of a gene (Tt)
Homologous
The chromosomes in a pair contain the same alleles of a gene (TT or tt)
Heterozygous The type of genes an organism has e.g. TT, Tt, tt
Homozygous
A study of the way parents pass characteristics on to their offspring
Meiosis
Cell division, produces cells for growth and repair
Mitosis
Unspecialised cells, capable of differentiating into other cell types
Phenotype
Controls the development of a characteristic only if a dominant gene is
not present
Polydactyly
Physical characteristics of an organism e.g. blue eyes, long tail
Recessive
Cell division, produces cells for sexual reproduction
Stem Cells
Condition of more than 5 toes or fingers, caused by a dominant allele
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Curriculum 2011 – AQA Additional Science
Questions.
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Biology workbook
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Curriculum 2011 – AQA Additional Science
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Biology workbook
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Curriculum 2011 – AQA Additional Science
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Curriculum 2011 – AQA Additional Science
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Wellsway school science dept.
Curriculum 2011 – AQA Additional Science
Biology workbook
AQA past paper question
3 In the 1850s, Gregor Mendel carried out breeding experiments using peas.
(a) The importance of Mendel’s work was not recognised until the early 1900s.
Explain why.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
(2 marks)
(b) A student repeated one of Mendel’s experiments.
The flow chart shows her procedure.
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Curriculum 2011 – AQA Additional Science
Biology workbook
The diagram shows a representative sample of seeds produced by second generation
plants.
(i) Describe how the student could obtain a sample that is representative of seeds
produced by the second generation.
..................................................................................................................................
..................................................................................................................................
(1 mark)
(ii) What was the approximate ratio of yellow seeds to green seeds in the seeds produced
by the second generation?
..................................................................................................................................
(1 mark)
(iii) Seed colour in peas is controlled by a single gene which has two alleles.
Use a genetic diagram to show why this ratio of yellow seeds to green seeds was
produced by the second generation.
Use the symbol A to represent the dominant allele, and a to represent the recessive
allele.
(4 marks)
(H PAPER – JAN 2008)
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6 The diagram shows a family tree in which some individuals have an inherited disorder,
which may cause serious long-term health problems.
6 (a) What proportion of the children of A and B have the disorder?
............................................................................................................................................
(1 mark)
6 (b) Explain the evidence from the diagram which shows that the allele for the disorder is
dominant.
Use the appropriate letters to identify individuals in your answer.
You may use genetic diagrams in your explanation. There is space below for you to draw
a genetic diagram.
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
(3 marks)
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Curriculum 2011 – AQA Additional Science
Biology workbook
6 (c) (i) What is meant by embryo screening?
..................................................................................................................................
..................................................................................................................................
(1 mark)
6 (c) (ii) A doctor suggests that couple C and D should have their embryos screened but
that couple G and H do not need this procedure.
Explain the reasons for the doctor’s suggestions.
..................................................................................................................................
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..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
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..................................................................................................................................
(3 marks)
(H PAPER – JAN 2009)
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Biology workbook