Genetics Practice Problems

Genetics Practice Problems

1. A brown mink, when crossed with a silver-blue mink produced all brown offspring. When these F1 mink were crossed among themselves they produced 47 brown animals and 15 silver-blue animals (F2 generation). Determine all the genotypes and phenotypes, and their relative ratios, in the F1 and F2 generations

2. A brown mouse is mated with two female black mice. When each female has produced several litters of young, the first female has had 48 black and the second female has had 14 black and 11 brown young. Determine the pattern of inheritance of coat colour and the genotypes of all the parents

3. In turkeys, a dominant gene R produces the familiar bronze colour; its recessive allele r results in red. Another dominant gene H results in normal feathers; its recessive allele h produces feathers without webbing, so that they resemble tufts of hair. Two bronze turkeys with normal feathers were mated, and their offspring consisted of 9 bronze with normal feathers, 3 bronze with hairy feathers, 3 red with normal feathers, and 1 red with hairy feathers. What were the genotypes of the parents?

4. In horses, black is dependent upon a dominant gene, B, and chestnut upon its recessive allele, b. The trotting gait is due to a dominant allele T, and the pacing gait to its recessive allele, t. If a homozygous black pacer is mated to a homozygous chestnut trotter, what will be the appearance of the F1 generation?

5. Yellow guinea pigs crossed with white ones always produce cream coloured offspring. Two cream coloured guinea pigs when crossed produced yellow, cream and white offspring in the ratio of 1 yellow:2 cream: 1 white. How are these colours inherited?

6. In humans, the blood groups are produced by various combinations of three alleles IA, IB , and IO. Blood types A and B are codominant and both and both A and B are dominant over O. Suppose a child is of blood type A and the mother is of type O. What type or types may the father belong to?

7. A mother and father with normal colour vision produce six male children, two of whom exhibit red-green colourblindness. Their five female children exhibit normal colour vision. Ignoring the fact that these parents ought to seek some family planning advice, explain the inheritance of red-green colourblindness in their male children.

8. A cross between a black cat and a tan cat produces a tabby pattern (black & tan fur together).

a) What pattern of inheritance does this illustrate?

b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

9. In squash, a gene for white colour (W) is dominant over its allele for yellow colour (w). Give the genotypic and phenotypic ratios for the results of each of the following crosses:

a) WW x ww

b) Ww x ww

c) Ww x Ww

10. If pollen from anthers of a heterozygous white-fruited squash plant is placed on the pistil of a yellow-fruited plant show, using ratios, the genotypes and phenotypes you would expect the seeds from this cross to produce.

11. In human beings, brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man marries a brown-eyed woman whose father was blue-eyed. What proportion of their children would you predict will have blue eyes?

12. A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a blue-eyed woman whose father and mother were both brown-eyed. The couple has a blue-eyed son. For which of the individuals mentioned can you be sure of the genotypes? What are their genotypes? What genotypes are possible for the others?

13. If the litter resulting from the mating of two short-tailed cats contains three kittens without tails, two with long tails, and six with short tails. What would be the simplest way of explaining the inheritance of tail length in these cats? Show genotypes.

14. When Mexican Hairless dogs are crossed with normal-haired dogs, about half of the pups are hairless and half have hair. When, however, two Mexican Hairless dogs are mated, about a third of the pups produced have hair, about two thirds are hairless, and some deformed puppies are born dead. Explain these results. Show genotypes.

Monohybrid Cross

1. A purple-flowered pea plant is crossed with a white-flowered pea plant. All the F1 plants produce purple flowers. When the F1 plants are crossed with each other, 401 of the F2 plants have purple flowers and 131 have white flowers. What are the genotypes of the parental and F1 generation plants?

2. In tomatoes, red fruit colour is dominant to yellow. Suppose a tomato plant homozygous for red is crossed with one homozygous for yellow. Determine the appearance of

(a) the F1

(b) the F2

(c) the offspring of a cross of the F1 back to the original red parent

(d) the offspring of a cross of the F1 back to the yellow parent

3. A red-fruited tomato plant, when crossed with a yellow-fruited one, produces progeny about half of which are red-fruited and half are yellow-fruited. What are the genotypes of the parents?

4. In guinea pigs, rough coat (R) is dominant over smooth coat (r). A rough-coated guinea pig is bred to a smooth one, giving 8 rough and 7 smooth progeny in the F1.

a) What are the genotypes of the parents and their offspring?

b) If one of the F1 animals is mated to its rough parent, what progeny would you expect?

5. Purple flowers are dominant to white flowers in the Jimsonweed. When a particular purple-flowered Jimsonweed is self-pollinated, there are 28 purple-flowered and 10 white flowered progeny. What proportion of the purple-flowered progeny are true-breeding?

Multiple Alleles

1. In rabbits, C=agouti coat colour, cch=chinchilla, ch=Himalayan, and c=albino. The four alleles constitute a multiple allelic series. The agouti is dominant to the other three alleles and albino à c is recessive to the other three alleles. Chinchilla is dominant to Himalayan. Determine the phenotypes of progeny from the following crosses.

a) CC X cc

b) Ccch X Cc

c) Cc X Cc

d) Cch X chc

e) Cch X cc

f) Cchch X chc

Codominant Alleles

1. In humans the three alleles IA, IB, and I constitutes a multiple allelic series that determine the ABO blood group system. For the following problems state whether the child mentioned can actually be produced from the marriage. EXPLAIN YOUR ANSWER.

a) an O child from the marriage of two A individuals

b) an A child from the marriage of an A to a B

c) an AB child from the marriage of an A to an O

d) an O child from the marriage of an AB to an A

e) an A child from the marriage of an AB to a B

Dihybrid Cross

1. In Jimsonweed purple flower (P) is dominant to white (p), and spiny pods (S) are dominant to smooth (s). In a cross between a Jimsonweed homozygous for white flowers and spiny pods and one homozygous for Purple flowers and Smooth pods, determine the following:

a) the phenotype of the F1

b) the phenotype of the F2

c) the progeny of a cross of the F1 back to the white, spiny parent

d) the progeny of a cross of the F1 back to the purple, smooth parent

2. What phenotypes would you expect to find in progeny from the following Jimsonweed crosses?

a) PPss X ppSS

b) PpSS X ppss

c) PpSs X PpSS

d) PpSs X PpSs

e) PpSs X Ppss

f) PpSs X ppss

3. In summer squash white fruit (W) is dominant over yellow (w), and disk-shaped fruit (D) is dominant over sphere-shaped fruit (d). In the following problems, the phenotypes of the parents and their offspring are given. Determine the genotypes of the parents in each case.

Parents

a) White, disk X Yellow, sphere

b) White, sphere X White sphere

c) Yellow disk X White sphere

d) White disk X Yellow sphere

Offspring

½ White disk and ½ white sphere

¾ White sphere and ¼ yellow

sphere

all white disk

¼ White disk, ¼ White sphere,

¼ Yellow disk, ¼ Yellow sphere