Question: When Thomas Hunt Morgan crossed his red-eyed F1 generation with flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

Answer: The gene involved is on the X chromosome.

Question: Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

Answer: Drosophila genes cluster into 4 distinct groups of linked genes.

Question: Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?

Answer: Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.

Question: A woman is found to have 47 chromosomes, including 3 X chromosomes. Which of the following describes her expected phenotype?

Answer: Normal female.

Question: Male are more often affected by sex-linked traits than females because…

Answer: Males are hemizygous for the X chromosome.

Question: SRY is best described in which of the following ways?

Answer: A gene region present on the Y chromosome that triggers male development.

Question: In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

Answer: Tortoiseshell females; black males.

Question: Red-green color blindness is a sex-linked trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

Answer: XCXc and XCY.

Question: Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

Answer: 100%.

Question: Calico cats are female because…

Answer: A male inherits only one of the two X-linked genes controlling hair color.