Biology 101: Additional practice genetics problems
These will not be collected
In the fruit fly Drosophila, normal wings (W) are dominant to vestigial (w), and normal
ocelli (N) are dominant to white ocelli (n). Note: vestigial means shrunken and
nonfunctional; “ocelli” are the tiny single-facet eyes located between their two large
compound eyes.
1. If a male fruit fly with vestigial wings mates with a female heterozygous normal fly:
A. What are the genotypes of the gametes each of the parents can produce?
Dad: ________________
Mom: ________________
B. What percentage of their offspring can fly? __________
2. A male, vestigial winged fly with normal ocelli mates with a female, normal winged fly with
white ocelli and among their offspring are approximately equal numbers of normal and vestigial
young, all with normal ocelli.
A. What are the genotypes of the parents and the offspring?
Dad: __________________ Mom: _________________
Offspring with Normal wings : ____________
Vestigial wings: ______________
B. What are the genotypes of the gametes the parents produced?
Dad: ________________________
Mom: _____________________
C. Draw a Punnett square that shows the observed result.
3. In radishes, the enlarged root is the edible part of the plant. Root shape determined by
incompletely dominate alleles elongated (E) and round (e). Root color is determined by the
codominant alleles red (R) and white (r).
A. Since the shape alleles are incompletely dominant, which one of these root phenotypes is
likely to occur for an Ee plant?
1) highly irregular knobby and bumpy roots; 2) oval-shaped roots, or 3) un-enlarged roots.
Explain.
B. Since the root color alleles are codominant, would a heterozygote with pink or brown
roots be most likely? Explain.
C. Assume that plants heterozygous for both traits are crossed. Using the product rule,
calculate the percentage of the offspring that will be ‘Eerr’.
4. Assume that height in humans is determined by 2 polygenic genes (T and S).
A. If the dominant alleles for each gene have an additive effect upon tallness, what would
be the genotype of tallest and shortest individuals?
Tallest: _________________
Shortest: ______________________
B. What is the number of possible different phenotypes?
C. If a mating occurred between persons heterozygous for each gene, what fraction of the
children would be expected to be the same height as their parents?
5. Mary has type A blood, and her mother has type B. Bob has type B blood, and his
mother was type A.
A. Draw a pedigree that shows the genotypes (as well as can be determined) of Mary and Bob
and their parents.
B. What are the possible genotypes and phenotypes of the fathers of Bob and Mary?
Bob’s father: _____________________________
Mary’s Father: _______________________________
C. Draw a Punnett Square that predicts the possible genotypes and phenotypes among Bob
and Mary’s children?
In humans, assume that brown eyes (B) are dominant over blue eyes (b); and that righthandedness (R) is dominant over left-handedness (r). Pseudohypertrophic muscular
dystrophy (PMD), a sex-linked disorder, causes progressive deterioration of muscles and is
usually fatal in the early teenage years. The alleles are designated as XP (normal) and Xp
(pseudohypertrophic).
6. A right-handed, blue-eyed man marries a right-handed brown-eyed woman. They have two
children, one left-handed and brown-eyed, the other right-handed and blue eyed. By a later
marriage, to a woman who is also right-handed and brown-eyed, this man has nine children, all
of whom are right-handed and brown eyed. Determine the probable genotypes for all individuals
mentioned. Write “ ? ” where an allele cannot be determined exactly.
Man: _________
First wife: _________
Second wife: _________
Child 1: ________
Child 2: __________
9 children: _________________________
7. Suppose a blue-eyed female carrier for PMD marries a normal male heterozygous for brown
eyes.
A. What are genotypes of the parents?
Mom: ________________________
Dad: ________________________
B. What are the genotypes of the gametes each parent will produce?
Mom: ________________________
Dad: ________________________
C. When their children reach adulthood, what is the expected frequency of blue-eyed males
and blue-eyed females?