Biology 190 - Genetics Problems - Set 2
Due by Tuesday, November 6 at 11:59 pm
1. The chances of an individual child being male or female are essentially 50:50.
If a man and a woman plan to have three children, what are the chances that
a. The second child will be male?
b. Two or more children will be female?
c. All three children will be male?
If a man and a woman plan to have five children, what are the chances that
d. Three will be female?
e. Four or more will be male?
f. Two or fewer will be female?
2. Eye color in mice is controlled by a single gene with two alleles, G and g. Animals with the
dominant allele have brown eyes, while those lacking the dominant allele have gray eyes.
If mating occurs between two heterozygous individuals
a. What will be the expected phenotype ratio in their F1 offspring?
For the same mating, what are the chances that
b. Their first two offspring both will have brown eyes?
c. Their first two offspring will include one with brown eyes and one with gray eyes?
d. Their first three offspring all will have gray eyes?
e. Two of their first three offspring will have brown eyes?
f. Two or more of their first three offspring will have gray eyes?
g. Every individual in a litter of four offspring will have brown eyes?
3. Color blindness in humans is an X-linked recessive trait. A color blind man and his wife who
is not color blind have two daughters, neither of them color blind. If one of the daughters
marries and has a male child, what are the chances that the boy will be color blind if the
boy’s father is:
a. Color blind?
b. Not color blind?
4. Pattern baldness in humans is a sex-influenced trait. The allele that causes pattern baldness is
dominant in men but recessive in women. If a man develops pattern baldness but his
father and mother had normal hair, what must be true about his mother’s genotype?
5. Blood type in humans is determined by two alleles, IA and IB, that exhibit codominance. A
person with IA but not IB will have type A blood, a person with IB but not IA will have type
B, people with both alleles are type AB and people with neither allele are type O. A man
with type A blood marries a woman with type B blood. What are the parents’ genotypes
if they have children with the following blood types:
a. Type A and Type AB
b. Type AB and Type B
c. Type A and Type O
d. Type A, Type B, Type AB and Type O
6. Scale color in goldfish exhibits additive polygenic inheritance at four unlinked loci, with two
incompletely dominant alleles at each locus. The darkest individuals in the population
are AABBCCDD, while the lightest individuals are aabbccdd. Other combinations (e.g.
AaBBCcdd) produce F1 individuals with intermediate coloration. A “darkest” individual
is crossed with a “lightest” individual, and the resulting offspring are intermediate in
coloration. If two of these intermediate F1 offspring are crossed, what are the chances of
an F2 individual having
a. The same phenotype as the darker grandparent?
b. The same phenotype as one of the two grandparents?
c. The same phenotype as its two F1 parents?
7. Hair color in guinea pigs is controlled by a single locus with two alleles. The dominant allele
B produces black hair while the recessive allele b produces guinea pigs with brown hair.
A population of 500 guinea pigs is in Hardy-Weinberg equilibrium.
a. What is the frequency of heterozygous guinea pigs if the population contains 80 brown
animals?
b. What is the frequency of the recessive allele b if the population contains 375 black animals?
c. How many homozygous dominant individuals would you expect to find if the population
contains five brown guinea pigs?
8. Flower color in morning glories exhibits 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 morning glories in Hardy-Weinberg
equilibrium?
a. 81% red-flowered plants and 1% white-flowered plants
b. 49% red-flowered plants and 42% pink-flowered plants
c. p = 0.4 and 48% pink-flowered plants
d. p = 0.25 and 56.25% white-flowered plants
e. 400 plants, 100 of which have red flowers and 100 of which have white flowers
f. 600 plants, 216 of which have white flowers and 288 of which have pink flowers
g. p = 0.15 and 500 plants, 75 with red flowers