BIRKBECK

(University of London)

B.Sc. EXAMINATION FOR INTERNAL STUDENTS

SCHOOL OF BIOLOGICAL AND CHEMICAL SCIENCES

ESSENTIALS OF GENETICS – BCBC006H5

15 CREDITS

TUESDAY, 26 MAY 2009 – 14.30 to 16.30

There are three sections. You should spend approximately the same time on
each section.

Complete Section A on the answer sheet provided on page 11 (instructions

on page 10) and Sections B and C in a normal answer book.

PUT YOUR CANDIDATE NUMBER AT THE TOP OF EACH ANSWER

SHEET / BOOK WHERE INDICATED.

Section A is a multiple choice test with 20 questions. There is only one correct
answer for each question. Answer all questions. You will not be penalised for
an incorrect answer. Each correct answer will be awarded 2 marks out of a
total of 40 marks.

Section B is a problem in Mendelian Genetics valued at a total of 30 marks.

Section C requires an essay type answer valued at 30 marks.

Use diagrams where appropriate.

No supplementary materials have been provided; calculators are not required.

This paper is not prior-disclosed.

©Birkbeck College 2009

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Section A

1. Crossing spherical-seeded pea plants with dented-seeded pea plants

resulted in progeny that all had spherical seeds. This indicates that the
dented-seed trait is:

a. dominant and the plants are homozygous for seed shape

b. codominant and the plants are homozygous for seed shape
c. codominant and the plants are heterozygous for seed shape
d. recessive and the plants are heterozygous for seed shape
e. recessive and the plants are homozygous for seed shape

2. If big feet (B) in rabbits is dominant to small feet (b), what is the genotype
of a big-footed rabbit with respect to the foot gene?

a. Bb
b. BB
c. bb or Bb
d. Bb or BB
e. bb or BB

3. An F1 pea plant which is pink flowered and has green pods is

heterozygous for both the flower colour and pod colour genes with the
genotype (PpGg). Its parents are:

a. PpGg and ppgg

b. PPGG and ppgg
c. PPgg and ppGG
d. PpGg and ppgg or PPGG and ppgg
e. PPGG and ppgg or PPgg and ppGG

4. If Mendel's crosses between tall, spherical-seeded plants and short,

dented-seeded plants, produced many more than 1/16 dented-seeded,
short plants in the F2 generation, he might have concluded that:

a. the spherical seed and tall traits are linked

b. the dented seed and short traits are unlinked
c. all traits in peas assort independently of each other
d. all traits in peas are linked
e. he would not have concluded any of the above

5. Among native Americans two types of earwax are seen, dry and sticky. A
geneticist observed the offspring produced by different kinds of matings.

Parents Offspring
Number of mating Sticky Dry
pairs
Sticky x sticky 10 32 12
Sticky x dry 8 21 19
Dry x dry 12 0 42

©Birkbeck College 2009

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Section A (continued)

How is earwax inherited?

a. Dry is dominant
b. Dry is recessive
c. Dry and sticky are codominant
d. Dry and sticky are different genes
e. Dry and sticky are X-linked

6. In humans a dimple in the chin is an autosomal dominant characteristic. A

man who does not have a chin dimple marries a woman with a chin dimple
whose mother lacked the dimple. What proportion of their children would
be expected to have a chin dimple?

a. 0.0
b. 0.25
c. 0.5
d. 0.75
e. 1.0

7. Two normal parents have an albino child. What are the parents
genotypes?

a. Both are homozygous for the albinism gene

b. One is heterozygous and one homozygous for the albinism gene
c. Both are heterozygous for the albinism gene
d. One is heterozygous for the albinism gene and one is homozygous
normal
e. Both are homozygous normal

8. Which statement about the inheritance of coat colour in rabbits is most

likely to be correct?

a. Brown is dominant to white

b. White is dominant to brown
c. Brown is produced by a cross between black and white
d. White and brown are codominant
e. You cannot reach any conclusions

9. When reciprocal crosses produce identical results,

a. the trait is not sex-linked

b. the trait is sex-linked
c. the trait is not autosomal
d. the trait is neither autosomal nor sex-linked
e. the trait is both sex-linked and autosomal

©Birkbeck College 2009

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Section A (continued)

10. In Mendel's experiments, the green seed character (GG) is completely

dominant over the yellow seed character (gg). If the characters for height
were incompletely dominant, such that TT are tall, Tt are intermediate, and
tt are short, what would be the result of crossing a green-seeded, short
(GGtt) plant to a dented-seeded, tall (ggTT) plant? These traits are linked.

a. All the progeny would be green-seeded and intermediate height

b. All the progeny would be green-seeded and tall
c. All the progeny would be green-seeded and short
d. 1/2 would be green-seeded and intermediate height; 1/2 would be
green-seeded and tall
e. You cannot predict the outcome

11. Galactosemia is a recessive human disease. A woman and her husband

are both heterozygous for the glactosemia gene. She has identical twins.
What is the probability that they are both girls and have galactosemia?

a. 0.0625
b. 0.125
c. 0.25
d. 0.5
e. 0.75

12. The achoo syndrome (sneezing in response to sunlight) and trembling

chin syndrome (triggered by anxiety) are both dominant human traits.
What is the probability that the first child of parents who are heterozygous
for both genes will have the achoo syndrome but not the trembling chin?

a. 0.0625
b. 0.125
c. 0.1875
d. 0.25
e. 0.5

13. A man in his 20s has learnt that his father has Huntington’s disease. What
is the probability that he will get the disease and that his son will get the
disease?

a. 1.0 and 0.5

b. 0.5 and 0.5
c. 0.5 and 0.25
d. 0.25 and 0.25
e. 0.25 and 0.125

©Birkbeck College 2009

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Section A (continued)

14. A highly inbred variety of domestic cow has no heritability for the amount
of milk produced. This means:

a. milk production is not under genetic control

b. there is no genetic variation for milk production between cows
c. the diet and other aspects of the environment only determine how
much milk is produced
d. a and b are correct
e. a and c are correct

15. A chromosome with the centromere in a central position is described as:

a. bivalent
b. karyotypic
c. centromeric
d. metacentric
e. tetraploid

16. Haploid chromosome numbers are n = 23 in humans and n = 24 in

chimpanzees. This is a consequence of what event in the ancestral
human lineage:

a. centric fusion of ape chromosomes 12 and 13

b. translocation between chromosomes 12 and 13
c. loss of the ape chromosome 13
d. polyploidy
e. a paracentric inversion in chromosome 13

17. The standard genetic model for the determination of human eye colour
proposes two unlinked genes Bey2 with brown and blue alleles and Gey
with green and blue alleles. People with green eye colour may be:

a. heterozygous at both genes

b. heterozygous at the Bey gene and homozygous at the Gey gene
for the green allele
c. homozygous at both genes for the blue allele with epistasis
d. homozygous at the Bey2 gene for the blue allele and have at least
one green allele at the Gey gene
e. b. and d. are both correct

©Birkbeck College 2009

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Section A (continued)

18. Orange coat colour in cats is X-linked. The orange and black pattern in
female Calico cats is an example of:

a. variation in expressivity
b. variable penetrance
c. epistasis
d. co-dominance
e. genetic mosaicism

19. In Drosophila Lyra (Ly) and Stubble (Sb) are dominant mutations on
chromosome 3. A recessive mutant with bright red eyes is discovered and
shown also to be on chromosome 3. Crossing a female who is
heterozygous for all three mutations to a male that is homozygous for the
bright red mutation (br) produces the following result.

Phenotype Number
Ly Sb br 404
+ + + 422
Ly + + 18
+ Sb br 16
Ly + br 75
+ Sb + 59
Ly Sb + 4
+ + br 2
1000

The chromosome map distance between Ly and Sb is:

a. 0.168 m.u.
b. 0.134 m.u.
c. 0.93 m.u.
d. 16.8 m.u.
e. 13.4 m.u.

20. The genes that control the fate of segments along the anterior-posterior
axis in animals are called:

a. gap genes
b. pair-rule genes
c. segment polarity genes
d. homeotic or Hox genes
e. Dlx genes

©Birkbeck College 2009

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Section B

Answer ALL of the following

“Normal” foxglove plants have the following phenotypes:

tall
pink petals
bilaterally symmetrical (“normal”) flowers

A “mutant” foxglove plant is detected with the following phenotypes:

dwarf
white petals
radially symmetrical (“peloric”) flowers.

Both normal plants and the mutant plant produce progeny identical to their
parent when they are selfed.

When crossed the normal and mutant parents produce an F1 which has all
tall, white-petaled and bilaterally symmetrical “normal” flowered progeny.

The F1 is test-crossed to a triply homozygous dwarf, pink, peloric plant and

produces the following phenotypes.

Phenotype Observed
Dwarf, White, Peloric 300
Tall, Pink, Normal 286
Dwarf, White, Normal 111
Tall, Pink, Peloric 121
Dwarf, Pink, Normal 85
Tall, White, Peloric 78
Dwarf, Pink, Peloric 10
Tall, White, Normal 9
1000

a) Are the parent plants homozygous or heterozygous? (1 mark)

b) What are the genotypes of the parental and F1 plants? (3 marks)

Use the following symbols for each gene:

D and d for the alleles controlling height

W and w for the alleles controlling petal colour
P and p for the alleles controlling flower shape

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c) If the genes were completely linked, what is the genotype of the gametes
that would be produced by the F1 (2 marks) and what number of progeny
plants of each phenotype would you have expected to observe in the
progeny of the test cross ? (3 marks)

d) Why does the expected number of plants of each phenotype depart from
the observed numbers you have listed above? (4 marks)

e) How would you test statistically whether the ratio of observed phenotypes
departs statistically significantly from the expected ratios of phenotypes?
Provide the statistical formula but do not carry out the calculation. (5 marks)

f) The genes are linked on the same chromosome. How far apart are the
genes for flower colour, flower shape and plant height? (6 marks)

g) What is the arrangement of genes for height, petal colour and flower
shape? (Draw the arrangement) (3 marks)

i) Is there any evidence of interference and if so why? (3 marks)

©Birkbeck College 2009

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SECTION C

Answer ONE question

1. What is meant by the terms ‘genotype’ and ‘phenotype’? (5 marks) Many

traits are said to have a genetic as well as an environmental component.
Explain this statement with reference to the heritability of continuously
varying (quantitative) traits. (25 marks)

2. Write an essay about sex determination. (30 marks)

3. Not all genetically inherited traits follow Mendelian ratios. Describe the
ways in which Non-Mendelian ratios are produced. (30 marks)

©Birkbeck College 2009

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Section A

Multiple Choice Question Answer Paper

Information about this part of the test

There are 20 questions. Complete as many of them as possible in the time
available.

You will not be penalized for wrong answers – if you do not know the
answer make an educated guess.

There is only ONE correct answer for each question.

Instructions
Write your candidate number at the top of the Answer Sheet.

For each question, place a cross in the column of the CORRECT answer.

Question A B C D E
No.
1 2

If you make a mistake or change your mind obliterate your first response by
shading the box out completely and then place a cross to show your revised
choice.

Question A B C D E
No.
1 z 2

©Birkbeck College 2009

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Section A: Answer sheet

Candidate Number:

Question
A B C D E
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

©Birkbeck College 2009

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