Workshop #10
 

APPENDIX D

GENETICS PROBLEMS

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

Ww x ww

Ww x Ww

2 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?

3. 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?

4. 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 .

5. A dominant gene, A, causes yellow color in rats. The dominant allele of another independent gene, R, produces black coat color. When the two dominants occur together (A/_ R/_), they interact to produce gray. Rats of the genotype a/a r/r are cream-colored. If a gray male and a yellow female, when mated, produce offspring approximately 3/8 of which are yellow, 3/8 gray, 1/8 cream, and 1/8 black, what are the genotypes of the two parents?

6. In Leghorn chickens colored feathers are due to a dominant gene, C; white feathers are due to its recessive allele, c. Another dominant gene, I, inhibits expression of color in birds with genotypes C/C or C/c. Consequently both C/_ I/_ and c/c _/_ are white. A colored cock is mated with a white hen and produces many offspring, all colored. Give the genotypes of both parents and off spring.

7. If the dominant gene K is necessary for hearing, and the dominant gene M results in deafness no matter what other genes are present, what percentage of the offspring produced by the cross k/k M/m x K/k m/m will be deaf?

8. If a man with blood type B, one of whose parents had blood type O, marries a woman with blood type AB, what will be the theoretical percentage of their children with blood type B?

9. Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs. Smith took home a baby girl, whom she named Shirley. Mrs. Jones took home a baby girl, whom she named Jane. Mrs. Jones began to suspect, however, that her child had been accidentally switched with the Smith baby in the nursery. Blood tests were made: Mr. Smith was type A, Mrs. Smith type B, Mr. Jones type A, Mrs. Jones type A, Shirley type O, and Jane type B. Had a mix-up occurred?

10. Suppose that gene b is sex-linked, recessive, and lethal. A man marries a woman who is heterozygous for this gene. If this couple had many normal children, what would be the predicted sex ratio of these children?

11. Red-green color blindness is inherited as a sex-linked recessive. If a color-blind woman marries a man who has normal vision, what would be the expected phenotypes of their children with reference to this character?

12. In Drosophila melanogaster the genes for normal bristles and normal eye color are known to be about 20 units apart on the same chromosome. Individuals homozygous dominant for these genes were mated with homozygous recessive individuals. The F1 progeny were then test-crossed. If there were 1,000 offspring from the test cross, how many of the offspring would you predict would show the cross-over phenotypes?

13. The crossover frequency between linked genes A and B is 40%; between B and C, 20%; between C and D, 10%; between C and A, 20 %; between D and B, 10%. What is the sequence of the genes on the chromosome?

14. There are three coat colors in certain breeds of horses: cream, palomino, and chestnut. If the chestnut and cream are crossed, only palomino are produced. If a palomino is crossed with either cream or chestnut, half the offspring will be palomino and half will be the color of the other parent. Explain the mode of inheritance. Give genotypic and phenotypic ratios for the following crosses: palomino x palomino, chestnut x chestnut, and chestnut x palomino.

15. If AabbCcDDEe X AaBbccDdee, what is the expected proportion of offspring that will be aabbccDdee?

16. In chickens, CC is normal, Cc results in a chicken with abnormally-short right legs called creeper, and cc is lethal. The incompletely dominant alleles B and b result in the following: BB black, Bb blue, and bb white. What are the expected genotypic and phenotypic ratios in the offspring when CcBb x Ccbb?

17. If a woman who had normal vision but whose father was color-blind married a man with normal vision, what are the chances that their son will be color-blind?

18. The allele B' for premature balding is dominant in males but recessive in females. The non-bald allele B is recessive in males but dominant in females. A bald man had a father and mother who were not bald. Give the genotype of the three people.

19. Give the genotypic and phenotypic ratios of the offspring produced from a man with type A blood whose father was type O and a woman with type AB.

20. The following results were produced in a test cross of AaBb X aabb:

AaBb 80

aaBb 12

Aabb 13

aabb 70

A. Draw the chromosomes of the AaBb individual indicating the position of the genes.

B. Determine the map distance between A locus and B locus.