1. Simple Mendelian Genetics
Practice Problems

3. Question #1
In rock pocket mice, dark color is recessive to light color. Write the genotypes and phenotypes for the following individuals:
Genotype
Phenotype
Heterozygous
Homozygous dominant
Homozygous recessive

4. Question #2
In rock pocket mice, dark color is recessive to light color.
If a rock pocket mouse who is a carrier for the mutation (but is light in color) mates with a light color mouse, what will be the genotypic and phenotypic ratios of their offspring?
If two of the heterozygous mice from the previous cross are mated, what will be the genotypic and phenotypic ratios of their offspring?

5. Question #3
A male with freckles, homozygous dominant, has offspring with a woman who does not have freckles. What are the genotypic and phenotypic ratios for their offspring?

6. Question #4
Believe it or not, having six fingers is dominant to having five fingers per hand. Usually the sixth digit is not fully formed and is amputated shortly after birth. A man and a woman, both heterozygous for the trait, want to have a child. What are the phenotypic ratios for their offspring?

7. Question #5
In humans, albinism is a recessive trait. What are the genotype and phenotype ratios of an albino woman and a normal-pigmented man whose mother was an albino?

8. Question #6
Neurofibromatosis is a dominant genetic disorder that causes tumors to grow along Schwann cells which insulate nerves and facilitate nerve impulse transmission. What are the genotypic and phenotypic ratios for a couple who are heterozygous and homozygous recessive?

9. Question #7
Cystic fibrosis is a recessive disorder where abnormally large amounts of mucus build up in the lungs, clogging airways and leading to inflammation and bacterial infections (among other symptoms). What is the chance of two heterozygous parents having two healthy children in a row?

10. Question #8
In pea plants, purple flowers are dominant to white flowers and yellow seeds are dominant over green seeds. A pea plant that is homozygous for purple flowers and heterozygous for yellow seeds is crossed with a pea plant with white flowers and is heterozygous for yellow seeds. What are the phenotypic ratios from this cross?

11. Question #9
A guinea pig that is heterozygous for black coat and rough coat is crossed with another guinea pig who is homozygous recessive for white coat and smooth coat. What are the phenotypic ratios of this genetic cross?