Genetics sample paper

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  • Created on: 02-04-16 11:14
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Genetics
b
Q1. Colour blindness is controlled by a gene on the X chromosome. The allele for colour blindness, X , is
B
recessive to the allele for normal colour vision, X . The gene controlling the presence of a white streak in the
hair is not sex linked, with the allele for the presence of a white streak, H , being dominant to the allele for the
absence of a white streak, h.
(a) Explain why colour blindness is more common in men than in women.
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(b) The diagram shows a family tree in which some of the individuals have colour blindness or have a white
streak present in the hair.
(i) What are the genotypes of individuals 5
and 6?
Individual 5
.............................................................................................................
Individual 6
.............................................................................................................
(2)
(ii) Give the possible genotypes of the gametes produced by
individual 5
.............................................................................................................
individual 6.
.............................................................................................................
(1)
(iii) What is the probability that the first child of individuals 5
and 6 will be a colour blind boy with a
white streak in his hair? Show your working.

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Answer ............................................
(2)
(Total 7 marks)
Q2. The production of pigment in rabbit fur is controlled by two genes.
One gene controls whether any pigment is made. This gene has three alleles. Allele A codes for the production
h
of one form of the enzyme tyrosinase, which converts tyrosine into a black pigment.…read more

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Total 9 marks)
Q3. A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat
produced 8 black kittens and 4 white kittens.
(a) (i) Explain the evidence that the allele for white fur is recessive.
.............................................................................................................
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(1)
(ii) Predict the likely ratio of colours of kittens born to a cross between this black male and a white
female.
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(1)
(b) The gene controlling coat colour has three alleles.…read more

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The breeder had expected equal numbers of chocolate and cinnamon kittens from the cross
between the chocolate male and black female. Explain why the actual numbers were different
from those expected.
.............................................................................................................
.............................................................................................................
(1)
(iv) The breeder wanted to produce a population of cats that would all have chocolate fur. Is this
possible? Explain your answer.
.............................................................................................................
.............................................................................................................
(2)
(Total 9 marks)
Q4.
People with night blindness have difficulty seeing in dim light.…read more

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Q5.S Redgreen colour blindness is caused by a mutation in the gene coding for one of the opsin proteins which
are needed for colour vision. The diagram shows the inheritance of redgreen colour blindness in one family.
Person 12 is pregnant with her fourth child. What is the probability that this child will be a male with redgreen
colour blindness? Explain your answer by drawing a genetic diagram.…read more

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Suggest one method by which the scientists could collect a random sample of ladybirds from the
trees.
.............................................................................................................
.............................................................................................................
(1)
Some of the results from the investigation are shown in the table.
Year Season Frequency of b allele
1933 Autumn 0.70
1934 Spring 0.82
1934 Autumn 0.59
1935 Spring 0.76
1935 Autumn 0.57
1936 Spring 0.78
(b) Use the HardyWeinberg expression to estimate the percentages of red ladybirds and black lady birds in
the Autumn 1933 ladybird population.
Show your working.
Answer ..................................................…read more

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The two genes are inherited independently but the effects of the alleles interact to produce three different
coat colours. The table gives four genotypes and the phenotypes they produce.
Genotype Phenotype
BbEe black
bbEe chocolate
Bbee yellow
bbee yellow
(a) What colour coat would you expect each of the following genotypes to give?
(i) BBEe ..............................
(ii) bbEE ..............................
(2)
(b) A BbEe
male was crossed with a b
bee female. Complete the genetic diagram to show the ratio of
offspring you would expect.…read more

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BbEe produces a black coat colour.
.............................................................................................................
.............................................................................................................
(2)
(Total 9 marks)
Q8. Human ABO blood groups are determined by the presence or absence of two antigens (A and B) on the
plasma membrane of the red blood cells.…read more

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Total 5 marks)
Q9. (a) (i) Explain what is meant by a
recessive allele.
.............................................................................................................
.............................................................................................................
.............................................................................................................
(1)
(ii) Explain what is meant by
codominant alleles.
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(1)
(b) The Rhesus blood group is genetically controlled. The gene for the Rhesus blood group has two alleles.
The allele for Rhesus positive,
R,
is dominant to that for Rhesus negative, r. The diagram shows the
inheritance of the Rhesus blood group in one family.…read more

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Show your working.
Answer .....................................................
(3)
(Total 9 marks)
Q10. Duchenne muscular dystrophy is a sexlinked inherited condition which causes degeneration of muscle
tissue. It is caused by a recessive allele. The diagram shows the inheritance of muscular dystrophy in one
family.
(a) Give evidence from the diagram which suggests that muscular dystrophy is
(i) sexlinked ...........................................................................................
.............................................................................................................
(1)
(ii) caused by a recessive allele. ...............................................................
.............................................................................................................…read more

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