For those of you who want more practice, here are some genetic problems:
GENETICS PRACTICE: BASIC MENDELIAN GENETICS
1. In humans the allele for albinism is recessive to the allele for normal skin pigmentation. If
two heterozygotes have children, what is the chance that a child will have normal skin
pigment? What is the chance that a child will be albino?
a. If the child is normal, what is the chance that it is
a carrier (heterozygous) for the albino allele? (CAREFUL!) ________________________
2. In purple people eaters, one-horn is dominant and no horns is recessive. Show the cross of
a purple people eater that is heterozygous for horns with a purple people eater that does not
have horns. Summarize the genotypes & phenotypes of the possible offspring?
3. In humans, the brown-eye (B) allele is dominant to the blue-eye allele (b). If two
heterozygotes mate, what will be the likely genotype and phenotype ratios of the offspring.
GENETICS PRACTICE: PROBABILITY PRACTICE
1. In humans, curly hair is dominant over straight hair. A woman heterozygous for hair curl
marries a man with straight hair and they have children.
a. What is the genotype of the mother? ______________________________________
b. What gametes can she produce?_________________________________________
c. What is the genotype of the father? _______________________________________
d. What gametes can he produce?__________________________________________
e. What is the probability that the 1st child will have curly hair?______________________
f. What is the probability that the 2nd child will have curly hair?______________________
2. List all the gametes that are possible with each of the following genotypes.
a. Aabb ___________________________ d. AABb ____________________________
b. AaBB ___________________________ e. AAbb ____________________________
c. AaBb ___________________________ f. aabb _____________________________
3. What is the probability of getting the gamete (ab) from each of the following parents?
a. Aabb ______________________________________________________________
b. aaBb ______________________________________________________________
c. AaBb ______________________________________________________________
d. AABb _____________________________________________________________
e. AAbb _____________________________________________________________
4. In a certain strain of mice, black coat (B) is dominant over white coat (b). Describe what you
would do to determine the genotype of a male with a black coat and how this would enable
you to choose between the genotypes BB or Bb.
GENETICS PRACTICE: BEYOND THE BASICS
1. In radishes, the gene that controls color exhibits incomplete dominance. Pure-breeding red
radishes crossed with pure-breeding white radishes make purple radishes. What are the
genotypic and phenotypic ratios when you cross a purple radish with a white radish?
2. Certain breeds of cattle show incomplete dominance in coat color. When pure breeding red
cows are bred with pure breeding white cows, the offspring are roan (a pinkish coat color).
Summarize the genotypes & phenotypes of the possible offspring when a roan cow is mated
with a roan bull
3. A man with type AB blood marries a woman with type B blood. Her mother has type O
blood. List the expected phenotype & genotype frequencies of their children.
10. The genes for hemophilia are located on the X chromosome. It is a recessive disorder. List
the possible genotypes and phenotypes of the children from a man normal for blood clotting
and a woman who is a carrier. (HINT: You have to keep track of what sex the children are!)