Biology 190 - Genetics Problems - Set 3
These are for practice and will not be graded.
1. The chances of an individual child being male or female are essentially 50:50.
If a man and a woman plan to have four children, what are the chances that
a. More than one child will be female?
b. They will have only one girl?
c. Half will be girls and half boys?
If a man and a woman have six children, what are the chances that
d. At least half will be boys?
e. The first three will be boys and the next three will be girls?
f. How many children must they have to have a 95% chance of at least one girl?
2. Seed color in garden peas is controlled by a single gene. The dominant allele, G, produces
plants with green peas, while homozygous recessive plants (gg) produce yellow peas.
You cross a heterozygous (Gg) plant with green peas and a plant with yellow peas. What
are the chances that
a. The first offspring will produce yellow peas?
b. The first three offspring will produce green peas?
c. Three or more of the first five offspring will produce green peas?
You cross two heterozygous plants. What are the chances that
d. At least half of the first six offspring will produce yellow peas?
e. None of the first 10 offspring will produce green peas?
3. Coat color in rabbits is determined by two unlinked loci. The first locus has two alleles.
Rabbits with the dominant allele, B, have brown fur, while homozygous recessive (bb)
individuals have gray fur. The second locus has two alleles and regulates synthesis of a
pigment-producing enzyme. Presence of the dominant allele, W, leads to pigmented
rabbits, while absence of the dominant allele leads to albinos.
A BbWw male is crossed with a homozygous albino (bbww) gray female.
a. What will be the expected phenotype ratio in their F1 offspring?
A brown male is crossed with a gray female. What are the possible genotypes of the two parents
if the offspring phenotype ratios are:
b. Brown:Albino = 3:1
c. Brown:Gray:Albino = 3:3:2
An albino male is crossed with a brown female. What are the possible genotypes of the two
parents if the offspring phenotype ratios are:
d. Brown:Gray = 3:1
e. Brown:Albino = 1:1
f. Albino:Brown:Gray = 4:3:1
4. Flower color in petunias shows incomplete dominance at a single locus with two alleles, R and
r. Homozygous dominant plants produce red flowers, heterozygous plants have pink
flowers and homozygous recessive plants produce white flowers. p is the frequency of
the dominant allele in the population and q is the frequency of the recessive allele. Are
the following populations of petunias in Hardy-Weinberg equilibrium?
a. 64% red-flowered plants and 32% pink-flowered plants
b. p = 0.15 and 25.5% pink-flowered plants
c. 400 plants, p = 0.5 and 200 with white flowers
d. q = 0.25 and 75% red-flowered plants
e. 600 plants, 54 with red flowers and 294 with white flowers
f. p = 0.35 and 54.5% with pink flowers
g. 800 plants, 480 with pink flowers.