Genetics Practice Problems
1. Explain how two black mice, when mated can produce some offspring that are white.
2. Apply the law of segregation to explain the kinds of gametes produced by an animal that has the genotype Aa.
3. One parent is homozygous for a certain trait, and the other is heterozygous. What fraction of their offspring would you expect to be heterozygous?
4. The offspring of a cross between two red-flowered plants show a ratio of 3 red-flowered plants to 1 white-flowered plant. Which trait is dominant? What must the genotypes of the parents be?
5. Watermelons with a round shape are crossed with those having a flatter shape. Some offspring have an oval shape. Explain.
6. In guinea pigs, rough coat (R) is dominant over smooth coat (r), and black (B) is dominant over albino (b). Make a Punnett square showing the ratio of different genotypes expected when a when a guinea pig having the genotype BbRr is crossed with one having genotype bbRr.
7. A man with blood type B marries a woman with blood type A. Their first child has blood type O. Explain. What other blood types are possible for their future children?
8. In fruit flies, the gene for red eyes (R) is dominant over the gene for white eyes (r) and is sex-linked. If an offspring is a white-eyes female, and her female parent has red eyes, what must be the genotype of her male parent be?
9. A cross between a homozygous red horse and a homozygous white horse produces an offspring with a coat color called roan. Examination of the roan’s coat reveals the presence of both red and white hairs. How is this pattern of inheritance explained? What results would you expect if two roan horses were crossed? How do you know that the genes controlling coat color are not completely dominant over each other?