Genetics Problems:

1) In guinea pigs, black fur is dominant over white fur. How could an animal breeder

test whether a black guinea pig is homozygous or heterozygous?

2) A short stem, yellow pod pea plant is crossed with a true breeding long stem, green

pod pea plant. Assuming that long stems are dominant to short stems, and green

pods are dominant to yellow pods 1) what are the genotypes and phenotypes of the

F1 generation? and 2) the genotypes and phenotypes from a F1 x F1 cross?

3) In humans, hemophilia (bleeder’s disease) is a recessive, sex-linked trait. Use a

Punnett square to show the possible genotypes of offspring of a man who is a

hemophiliac (X

h Y), and a normal, homozygous woman (XHX

H

), where XH

contains

the normal clotting gene and Xh

contains the gene for hemophilia.

4) Cystic fibrosis is a human disease caused by an autosomal recessive mutation.

About 1 in 22 people in the human population are heterozygous carriers and have no

symptoms of the disease. A woman who has a brother with CF marries a man who

has no history of CF in his family.

a) What are the possible genotypes of the woman?

b) What is the most likely genotype of the man?

c) What is the percentage of offspring that would be affected with CF, depending

upon the genotype of the mother?

5) Lesch-Nyhan syndrome is a metabolic defect caused by the lack of the enzyme

hypoxanthine-guanine phosphoribosyl transferase (HGPRT). This disease is the

result of an X-linked, recessive mutation and results in mental retardation, selfmutilation and early death. A normal man marries a woman who had a brother who

died of LNS. Your are the genetic counselor who will advise them on the likelihood

of their having a LNS baby.

a) What are the possible genotypes for the woman? What is the man’s genotype?

b) For each of the woman’s possible genotypes, what are the possible genotypes of

her offspring and the implications for survival for each of them?

6) A colorblind female, blood type A married 2 different men. One man (#1) had type

AB blood and was colorblind. The other man (#2) had type B blood and normal color

vision. Three offspring resulted from the marriages. If possible, determine the father

of each of the following offspring.

a) female, Type A blood, normal color vision

b) male, Type AB blood, colorblind

c) female, Type B blood, colorblind

7) In tomatoes, red fruit color is dominant to yellow. Suppose a tomato plant

homozygous for red is crossed with one homozygous for yellow. Determine the

phenotype and genotype of

a) the F1 offspring

b) the offspring of a cross of the F1 back to the red parent

c) the offspring of the F1 back to the yellow parent

8) In humans, the allele for free earlobes is dominant to the allele for attached earlobes.

A woman with attached earlobes has children with a man who has free earlobes.

a) what are the possible genotypes of the woman?

b) What are the possible genotypes of the man?

c) What proportion of their offspring will have attached earlobes?

9) Fur color in tribbles is determined by a pair of alleles B and b. BB and Bb tribbles

are black and bb tribbles are white.A white female tribble is bred with a black male

tribble. They have 15 white and 18 black baby tribbles. What is the genotype of the

male tribble?

10) Phenylketonuria (PKU) is a human genetic disorder in which the affected individual

cannot metabolize the amino acid phenylalanine. The disease is characterized by

severe mental retardation if left untreated. The disease is caused by homozygosity

for a recessive, mutant allele. If two parents are heterozygous for the allele, what is

the probability that their child will have PKU?

11) In one experiment, Mendel crossed a purple-flowered, tall plant that had come from a

previous hybridization (i.e., it was not true breeding) with a white-flowered, dwarf

plant. The results were as follows:

• Purple flowers, tall 47

• White flowers, tall 40

• Purple flowers, dwarf 38

• White flowers, dwarf 41

What are the genotypes of both parent plants and all of the 4 classes of progeny?

12) Two black female mice are crossed with the same brown male. In a number of litters

female X produced 9 blacks and 7 browns and female Y produced 14 blacks. Which

color is dominant and why? What are the genotypes of the parents?

13) A farmer breeds a chicken with all white plumage with a chicken with all black

plumage. All of the F1 offspring have bluish-gray plumage. When two of the bluishgray birds are crossed, black, white and bluish-gray offspring are produced. What is

the mechanism of inheritance and the genotypes of the parents, F1’s and F2’s.

14) A couple with a newborn baby is troubled that the child does not resemble either of

them. Suspecting that a mix-up occurred at the hospital, they check the blood type

of the infant and find that it is type O. As the father is type A and the mother type B,

they conclude that a mix-up must have occurred. Are they correct?

15) In the fruit fly, Drosophila melanogastrer, the allele for dumpy wings (d) is recessive

to the normal long-wing allele, (D) and the allele for white eye (w) is recessive to the

normal red-eye allele (W). In a cross of DDWW with Ddww, what proportion of the

offspring are expected to be “normal” (long wings and red eyes)? What proportion

are expected to have dumpy wings and white eyes?