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FACULTY OF HEALTH AND APPLIED SCIENCES

DEPARTMENT OF NATURAL AND APPLIED SCIENCES

QUALIFICATION: BACHELOR OF SCIENCE

QUALIFICATION CODE: 07BOSC LEVEL: 6

COURSE CODE: GEN602$ COURSE NAME: GENETICS

SESSION: NOVEMBER 2017 PAPER: THEORY

DURATION: 3 HOURS MARKS: 120

FIRST OPPORTUNITY EXAMINATION QUESTION PAPER

EXAMINER(S) Prof Percy Chimwamurombe

MODERATOR:Prof Sylvester Rodgers Moyo

INSTRUCTIONS

1. Answer ALL the questions.2. Write clearly and neatly.3. Number the answers clearly.

PERMISSIBLE MATERIALS

Non—programmable Calculators

ATTACH M E NTS

None

THIS QUESTION PAPER CONSISTS OF 6 PAGES (Including this front page)

SECTION A MULTIPLE CHOICE QUESTIONS [20 MARKS]

A1. In the lac operon, the 2 gene encodes for: (1)

(a) permease enzyme

(b) lactase protein

(c) beta galactosidase enzyme

(d) all of the above

A2. In the lac operon, the y gene encodes for: (1)

(a) permease enzyme

(b) lactase protein

(c) beta galactosidase enzyme

(d) none of the above

A3. Eukaryotic genes have (1)

(a) exons only

(b) introns only

(c) exons intervened with introns

(d) none of the above

A4. Which of the following is an example of a structural motif in transcription factors. (1)

(a) homeodomain

(b) leucine zipper

(c) POU domain

(d) all of the above

A5. If two pa rents carry the recessive gene of Cystic Fibrosis (c), that is,

they are heterozygous (Cc), What is the probability that one child of the parents

will not suffer from the disease (1)

(a) 1/z

(b) 0

(c) ‘/4

(d) %

A6. Genes show incomplete dominance when the heterozygous phenotype is (1)

(a) fuzzy

(b) like the dominant homozygote

(c) half way there

(d) none of the above

A7. In the F1 generation of a monohybrid cross, the phenotypic ratio would be: (1)

(a)&

w)1:2:1

(c)2:1:1

w)11:2

A8. Hemophilia is a sex-linked recessive trait in humans. If a father and a son are

both hemophiliacs, but the mother is normal, her genotype must be: (1)

(a) XhXh

(b) XHXh

(c) XHXH

(d) XhY

A9. Mitosis involves separation of only sister chromatids while meiosis involves? (1)

( ) Also separation of only sister chromatids.

(b) Separation of only homologous chromosomes.

( ) Separation of homologous chromosomes as well as sister chromatids.

( ) Separation of sister chromatids twice.

A10. An example of alleles is: (1)

(a) AB and Tt.

(b) TT and Tt.

(C) T and t.

(d) X and Y.

A11. Which blood type would not be possible for children of a type AB mother

and a type A father? (1)

>

.

P”AAAA Q.

0‘

vvvv m>oA12. Long radishes crossed with round radishes result in all oval radishes.

This type of inheritance is: (1)

(a) Multiple alleles.

(b) Complete dominance.

(C) Co-dominance.

(d) Incomplete dominance.

A13. If two white sheep produce a black offspring, the parent’s genotypes for colour must be: (1)

(a) Heterozygous.

(b) Homozygous white.

(0) Homozygous black.

(d) Not enough information was given.

A14. An extra finger in humans is rare but is due to a dominant gene. When one parent

is normal and the other parent has an extra finger but is heterozygous for the trait,

what is the probability that the first child will be normal? (1)

(a) 0%.

(b) 25%.

(c) 50%.

(d) 75%.

A15. In drosophila (fruit flies), eye colour is sex-linked and red eye colour is dominant

to white eye colour. Which of the following are not possible in a cross between a

red-eyed male and a heterozygous female? (1)

(a) Red-eyed male.

(b) White-eyed male.

(C) Carrier female.

(d) Homozygous white-eyed female.

A16. Which statement is true concerning a pair of alleles for a gene controlling a single characteristic

in humans? (1)

(a) Both genes come from the father.

(b) Both genes come from the mother.

(C) One gene comes from the mother and one gene comes from the father.

(d) The genes come randomly in pairs from either the mother or father.

A17. Genetic traits of seeds are noted as follows: (1)

L = long, I = short

W = wrinkled, w = smooth

Y = yellow, y= white

R = ribbed, r = groovedWhich of the following is the genotype for a short, wrinkled, yellow, grooved seed?

(a) lleyyrr

(b) LLWWyYRr

(c) LIWwYYRr

(d) lleYYrr

A18. Mendel discovered principles of inheritance because he: (1)

(a)

(b)

(C)

(d)

A19.

(8)

(b)

(C)

(0')

A20.

(8)

(b)

(C)

(d)

Observed simultaneously all of the many characteristics in which the parents differed.

Believed that the hereditary characteristics of two individuals became thoroughly blended in

the offspring.

Ignored all characteristics except a few markedly contrasting ones in which he studied.

Studied only the offspring obtained from a single mating.

Which of the following factors could lead to variations in the offspring of asexually reproducing

organisms? (1)

Crossing over.

Fertilization.

Mutations.

Independent assortment.

An example of a genotype is: (1)

A tall pea plant.

R and r.

TtHH.

Hemophiliac.

SECTION B [80 MARKS]

If a pure breeding strain of mice with brown coloured fur are allowed to breed with a pure strain

of mice with grey fur they produce offspring having brown-coloured fur. If the F1 mice are

allowed to interbred they produce an F2 generation with fur colour in the proportion of three

brown to one grey

(a) Explain these results fully. (5)

(b) What would be the result of mating a brown coloured heterozygote from

the F2 generation with the original grey coloured parent? (5)

Why is it not possible to use a homozygous dominant organism such as (TT) in a test

cross experiment to determine the genotype of an organism showing a

dominant phenotype? Illustrate your answer fully using appropriate genetic symbols. (10)

The ability to taste the chemical PTC is determined by a single gene in humans with

the ability to taste given by the dominant allele T and inability to taste by the

recessive allele t. Suppose two heterozygous tasters (Tt) have a large family.

(a). Predict the proportion of their children who will be tasters and nontasters.

Use a Punnett square to illustrate how you make these predictions. (6)

(b). What is the likelihood that their first child will be a taster? What is the likelihood

that their fourth child will be a taster?

lst child (1)4th child (1)

(c). What is the likelihood that the first three children of this couple will be nontasters? (2)

4. A rooster with grey feathers is mated with a hen of the same phenotype. Among their

offspring 15 chicks are grey, 6 are black and 8 are white.

(a). What is the simplest explanation for the inheritance of these colors in chickens? (5)

(b). What offspring would you expect from the mating of a grey rooster and a black hen? (5)

5. In a certain plant, blue (B) flower color is dominant to white (b). You have a

blue flowered plant and a white flowered plant.

(a). What do you know about the genotype and phenotype of each plant? (3)

(b). Now you cross the plants and all the offspring are blue. What have you learned

about the genotypes of the original plants? (2)

(c). Consider the blue-flowered plants produced from the above cross: what gamete

types will they produce? If you cross two of these blue-flowered plants to

produce a large number of offspring, what genotypes and phenotypes will be

produced and in what proportions? (5)

6. Describe promoter sequences in prokaryotes. (15)

7 Briefly explain the function of the trp operon in E.co/i. (15)

SECTION C [20 MARKS]

1. A plant heterozygous for three independently assorting gene, AaBch, is self-fertilised.

Among the offspring, predict the frequency of

(a) AABBCC individuals (4)

(b) aabbcc individuals (4)

(c) individuals that are either AABBCC or aabbcc (4)

(d) AaBch individuals (4)

(e) Individuals that are not heterozygous for all genes (4)

-------------------END OF EXAMINATION QUESTIONS-----—-------------