Download Chapter 8: Genetics

Chapters 23 & 24: Genetics
Practice Problems
Level 1
1. Color blindness, a sex-linked disorder, is a genetic disease. A female carrier and a
male with normal eyesight want to have children. What are the phenotypes of their
offspring?
2. Fur color in rabbits is an example of incomplete dominance. A rabbit with black fur
(BB) mates with a rabbit with white fur (bb). A genotype of Bb would produce gray
rabbits. What would the offspring look like?
3. Samantha has a son who is color blind, a sex-linked trait. She, however, is not color
blind. Show what her genotype must be, and what the genotype of her father could
be.
4. A man who is heterozygous for a chin cleft and homozygous dominant for a widow’s
peak mates with a woman who is heterozygous for a chin cleft and is homozygous
recessive with no widow’s peak. Chin cleft and widow’s peak are both dominant
traits. What are the parent genotypes? How many kids would have both a chin cleft
and a widow’s peak? (Dihybrid cross!)
5. Mom and Dad are both heterozygous for freckles and a widow’s peak (both dominant
traits). What will their children look like? (Dihybrid cross!)
6. One parent is homozygous for a certain trait, and the other is heterozygous. What
percent of their offspring would you expect to be heterozygous?
7. Jake has type B blood, and his brother John has type O blood. What are the possible
genotypes and phenotypes for their parents?
8. A pink snapdragon is crossed with a white snapdragon. What will the offspring look
like? (incomplete dominance)
9. Complete the punnett square: XBXB x XbY. (B = normal eyesight, b = blind) How
many of their daughters and sons would be blind?
10. Show how it would be possible for a generation of snapdragons to appear red, white,
and pink in color. (incomplete dominance)
11. How would it be possible for parents to have both a boy and a girl with a sex-linked
disease?
12. A man who is homozygous dominant for large ears and heterozygous for freckles has
children with a woman who is heterozygous for large ears and homozygous recessive
with no freckles. How many of their children would have large ears and no freckles?
(Dihybrid cross!)
13. If half the offspring have type A blood and half have type AB, what are the possible
parental genotypes and phenotypes?
14. A black guinea pig is crossed with a white guinea pig. Black is dominant. All of the
individuals in the F1 generation were black. These individuals were then crossed
among themselves, resulting in 30 black guinea pigs and 10 white ones in the F2
generation.
A. How many of the black guinea pigs in the F2 generation are homozygous
dominant?
B. How many of the black guinea pigs in the F2 generation are heterozygous?
C. How many of the white pigs in the F2 generation would be homozygous
recessive? Heterozygous?
15. What were the parents of the following offspring from guinea pig crosses? Give all
possibilities, assuming that the laws of chance operate. Black is dominant.
A. One half of the offspring are black.
B. Three-fourths of the offspring are black.
C. One half of the offspring are heterozygous (black).
D. All of the offspring were black.
E. All of the offspring were white.
F. One half of the offspring were white.
G. One fourth of the offspring were white.
16. Nine of ten children in a family are right-handed. Right-handedness is a dominant
trait. Assume that this trait is controlled by a single pair of genes and answer these
questions:
A. What is the genotype of the left-handed child?
B. What are the possible genotypes of the right-handed children?
C. What are the possible genotypes of the parents?
D. Could these parents have produced only right-handed children? Explain.
E. If these parents had produced only one child, would it have been left or righthanded? Explain.
17. A wealthy, elderly couple dies together in an accident. A man shows up at the
reading of the will, claiming the fortune they left behind. He contends that he is their
only son who ran away from home when a boy and is now entitled to the fortune.
Hospital records show that the deceased couple was of blood types AB and O. The
claimant proves to have type O blood. Does this information rule him out as a
claimant? Explain.
18. A woman bears a child out of wedlock and sues a particular man for support of the
child, claiming that he is the father. Blood typing shows that she is type A, her child
is type O, and the man is type B. The man says that this proves that he is not the
father, but the judge says that it proves no such thing. Was the accused man or the
judge correct? Support your answer with a punnett square.
19. Show how it would be possible for a couple to have children with straight, wavy, and
curly hair (incomplete dominance).
20. Mom is heterozygous for a particular trait. Dad is homozygous recessive. What are
the odds that they will have three children who are heterozygous?
21. A couple has three boys. What are the odds that they will have a boy the next time
they try to have a child?
22. What are the odds that a family will have five daughters born in a row?