Biology 2
Genetics Problems Assignment
Fall 2011 Due Weds 10/26
Turn in the solutions to each of the following genetics problems. You may use
any resources, including discussions with other students and your instructor, that
you find helpful in devising the solutions. Show your work and make sure your
answers can easily be identified, by highlighting, underlining or putting a circle
around the final results. Answers that appear to be copied from the papers of
other students will not receive credit.
1. Consider the following two separate autosomal genes that behave
independently. One gene specifies the presence of a chin cleft (indentation in
the chin). The autosomal dominant allele C causes a chin cleft while the
autosomal recessive allele c causes a smooth chin. Another gene influences
earlobe shape. The autosomal dominant allele E causes free earlobes while
the autosomal recessive allele e causes attached earlobes. Michael Douglas
has attached earlobes and a chin cleft. His wife, Catherine Zeta-Jones, has
free earlobes and a smooth chin. Michael and Catherine already have one son
with a chin cleft like his father’s. What are the expected phenotypes for future
children born to Michael and Catherine and what fraction of children will have
each phenotype? [Assume that Michael’s mother has a smooth chin and
Catherine’s father has attached earlobes.]
2. Hair curling is due to incompletely dominant alleles where allele H gives curly
hair, allele H’ gives straight hair and heterozygotes with the genotype HH’
have wavy hair. What are the phenotypes of children expected for each of the
following marriages and what fraction of children will have each phenotype?
a. Curly-haired male with Straight-haired female
b. Straight-haired male with Wavy-haired female
c. Wavy-haired male with Curly-haired female
3. In humans, ABO blood type is inherited with a single gene having multiple
alleles and codominance. Dominant allele A is for Type A blood, dominant
allele B is for Type B blood and recessive allele o is for Type O blood. A and B
are codominant and completely dominant over o. What are the phenotypes of
children expected for each of the following marriages and what fraction of
children will have each phenotype?
a. Type AB male with Type O female
b. Type B male (whose mother is Type O) with
Type A female (whose father is Type O)
c. Type AB male with Type AB female
4. In one study, human skin color was shown to be inherited as a polygenic trait
with contributions from two genes as shown in the table below.
Number of
Dominant Alleles
0
1
2
3
4
Skin Color
Genotypes
White
Light Black
Medium Black
Dark Black
Darkest Black
aabb
Aabb or aaBb
AAbb, aaBB or AaBb
AABb or AaBB
AABB
What are the phenotypes of children expected for each of the following
marriages and what fraction of children will have each phenotype?
a. Darkest Black Female with White Male
b. Light Black Female (Aabb) with Medium Black Male (AaBb)
c. Medium Black Female (AAbb) with Dark Black Male (AaBB)
d. Light Black Female (aaBb) with Light Black Male (Aabb)
5. In humans, Becker Muscular Dystrophy (BMD) is inherited with the X-linked
recessive allele b. Individuals with the X-linked dominant allele B do not have
the disease. What are the phenotypes of children expected for each of the
following marriages and what fraction of children will have each phenotype?
a. Evan has BMD. His wife Elaine does not have BMD. Elaine’s father,
however, has BMD. Predict phenotypes (including gender) and
fractions for Evan and Elaine’s children.
b. Fred does not have BMD. His wife Francine also does not have the
disease. Francine’s father, however, has BMD. Predict phenotypes
(including gender) and fractions for Fred and Francine’s children.
c. Lawrence does not have BMD. His wife Lillian has BMD. Predict
phenotypes (including gender) and fractions for Lawrence and Lillian’s
children.