Download Genetics Problems

GENETICS PROBLEMS
1. In one experiment, Mendel crossed a pea plant that was true breeding for green pods with one that was true
breeding for yellow pods. All the plants in the next generation had green pods. Which form of the trait (green or
yellow pods) is recessive? Explain how you arrived at your solution.
2. A woman with blue eyes (bb) marries a man who is heterozygous for eye color.
a. What is the chance that their first child will have blue eyes?
b. What is the chance that their first child will be a boy with blue eyes?
3. Two people with brown eyes have a child with blue eyes (bb).
a. What are the genotypes of the parents?
b. What is the chance that their next child will have brown eyes?
4. Use the second law of probability and several Punnet squares (if needed) to answer the following question: if you
cross two individuals with the following genotypes for 4 traits… AABbCcdd x AaBbccDD, what is the probability
that a child with the genotype AABBccDd will be produced?
5. A dominant allele W confers black fur to guinea pigs. If a guinea pig is homozygous recessive, it has white fur.
Fred would like to know whether his pet black-furred guinea pig is homozygous dominant or heterozygous.
Describe the typical way that a breeder would determine his genotype.
6. Red-flowering snapdragons are homozygous for the allele R. White flowering snap dragons are homozygous for
a different allele. Heterozygous plants bear pink flowers. What phenotypic ratios should appear among offspring
from the following crosses?
a. Red x pink
b. Pink x pink
c. White x pink
7. A mother has blood type O, her child has type A. The father could not have blood type(s) __________________.
GENETICS PROBLEMS
1. In one experiment, Mendel crossed a pea plant that was true breeding for green pods with one that was true
breeding for yellow pods. All the plants in the next generation had green pods. Which form of the trait (green or
yellow pods) is recessive? Explain how you arrived at your solution.
2. A woman with blue eyes (bb) marries a man who is heterozygous for eye color.
a. What is the chance that their first child will have blue eyes?
b. What is the chance that their first child will be a boy with blue eyes?
3. Two people with brown eyes have a child with blue eyes (bb).
a. What are the genotypes of the parents?
b. What is the chance that their next child will have brown eyes?
4. Use the second law of probability and several Punnet squares (if needed) to answer the following question: if you
cross two individuals with the following genotypes for 4 traits… AABbCcdd x AaBbccDD, what is the probability
that a child with the genotype AABBccDd will be produced?
5. A dominant allele W confers black fur to guinea pigs. If a guinea pig is homozygous recessive, it has white fur.
Fred would like to know whether his pet black-furred guinea pig is homozygous dominant or heterozygous.
Describe the typical way that a breeder would determine his genotype.
6. Red-flowering snapdragons are homozygous for the allele R. White flowering snap dragons are homozygous for
a different allele. Heterozygous plants bear pink flowers. What phenotypic ratios should appear among offspring
from the following crosses?
a. Red x pink
b. Pink x pink
c. White x pink
7. A mother has blood type O, her child has type A. The father could not have blood type(s) __________________.
8. Certain dominant alleles are so vital for normal development that an individual who is homozygous recessive for a
mutant recessive form of the allele cannot survive. Consider the Manx allele in cats. Homozygous cats die when
they are still embryos inside the mother cat. In heterozygotes the spine develops abnormally, and cats end up
with no tail whatsoever. If two heterozygote cats mate, among their surviving kittens, what is the probability that
any one kitten will be tailless?
9. Two parents are both phenotypically normal, but their son suffers from hemophilia, a sex-linked recessive
disorder.
a. Draw a pedigree that shows the genotypes of the three individuals.
b. What fraction of the couple’s children is likely to suffer from hemophilia?
c. What fraction is likely to be carriers?
10. Colorblindness is a trait that is sex linked (located on the X chromosome) in humans.
a. If a male child is colorblind, what possible genotypes could his parents have?
b. If a female child is colorblind, what possible genotypes could her parents have?
11. In dogs, black (B) is dominant to chestnut(b), and solid(S) is dominant to spotted(s). What are the genotypes of
the parents that would produce a cross with 3/8 black solid, 3/8 black spotted, 1/8 chestnut solid, and 1/8 chestnut
spotted puppies? Hint: these are two separate genes; ex. BbSs would be a black solid puppy.
12. Fur color in rabbits is determined by a single gene for which there is 4 possible alleles. Four phenotypes are
possible: black, Chinchilla (grey color caused by white hairs with black tips), Himalayan (white with black patches
on extremities), and white. The black allele (C) is dominant over all other alleles, the Chinchilla allele (C ch) is
dominant over Himalayan (Ch), and the white allele is recessive to all others.
a. A black rabbit is crossed with a Himalayan, and the F 1 consists of 2 black to 2 Chinchilla. Determine the
possible genotypes of the parents.
8. Certain dominant alleles are so vital for normal development that an individual who is homozygous recessive for a
mutant recessive form of the allele cannot survive. Consider the Manx allele in cats. Homozygous cats die when
they are still embryos inside the mother cat. In heterozygotes the spine develops abnormally, and cats end up
with no tail whatsoever. If two heterozygote cats mate, among their surviving kittens, what is the probability that
any one kitten will be tailless?
9. Two parents are both phenotypically normal, but their son suffers from hemophilia, a sex-linked recessive
disorder.
a. Draw a pedigree that shows the genotypes of the three individuals.
b. What fraction of the couple’s children is likely to suffer from hemophilia?
c. What fraction is likely to be carriers?
10. Colorblindness is a trait that is sex linked (located on the X chromosome) in humans.
a. If a male child is colorblind, what possible genotypes could his parents have?
b. If a female child is colorblind, what possible genotypes could her parents have?
11. In dogs, black (B) is dominant to chestnut(b), and solid(S) is dominant to spotted(s). What are the genotypes of
the parents that would produce a cross with 3/8 black solid, 3/8 black spotted, 1/8 chestnut solid, and 1/8 chestnut
spotted puppies? Hint: these are two separate genes; ex. BbSs would be a black solid puppy.
12. Fur color in rabbits is determined by a single gene for which there is 4 possible alleles. Four phenotypes are
possible: black, Chinchilla (grey color caused by white hairs with black tips), Himalayan (white with black patches
on extremities), and white. The black allele (C) is dominant over all other alleles, the Chinchilla allele (C ch) is
dominant over Himalayan (Ch), and the white allele is recessive to all others.
a. A black rabbit is crossed with a Himalayan, and the F 1 consists of 2 black to 2 Chinchilla. Determine the
possible genotypes of the parents.