Info

417 miniature

415 miniature

(d)

long

miniature

753 miniature

761 long

(e)

long

long

625 long

630 long

In chickens, congenital baldness results from a Z-linked recessive gene. A bald rooster is mated with a normal hen.

The F1 from this cross are interbred to produce the F2. Give the genotypes and phenotypes, along with their expected proportions, among the F1 and F2 progeny.

27. In the eastern mosquito fish (Gambusia affinis holbrooki), which has XX-XY sex determination, spotting is inherited as a Y-linked trait. The trait exhibits 100% penetrance when the fish are raised at 22°C, but the penetrance drops to 42% when the fish are raised at 26°C. A male with spots is crossed with a female without spots, and the F1 are intercrossed to produce the F2. If all the offspring are raised at 22°C, what proportion of the F1 and F2 will have spots? If all the offspring are raised at 26°C, what proportion of the F1 and F2 will have spots?

* 28. How many Barr bodies would you expect to see in human cells containing the following chromosomes?

29. Red - green color blindness is an X-linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has normal fingers and toes and normal color vision. Her mother is normal in all respects, but her father is color blind and polydactylous. Bill is color blind and polydactylous. His mother has normal color vision and normal fingers and toes. If Bill and Martha marry, what types and proportions of children can they produce?

* 30. Miniature wings in Drosophila melanogaster result from an

X-linked gene (Xm) that is recessive to an allele for long wings (X+). Sepia eyes are produced by an autosomal gene (s) that is recessive to an allele for red eyes (s+).

(a) A female fly that has miniature wings and sepia eyes is crossed with a male that has normal wings and is homozygous for red eyes. The F1 are intercrossed to produce the F2. Give the phenotypes and their proportions expected in the F1 and F2 flies from this cross.

(b) A female fly that is homozygous for normal wings and has sepia eyes is crossed with a male that has miniature wings and is homozygous for red eyes. The F1 are intercrossed to produce the F2. Give the phenotypes and proportions expected in the F1 and F2 flies from this cross.

31. Suppose that a recessive gene that produces a short tail in mice is located in the pseudoautosomal region. A short-tailed male is mated with a female mouse that is homozygous for a normal tail. The F1 from this cross are intercrossed to produce the F2. What will the phenotypes and proportions of the F1 and F2 mice be from this cross?

* 32. A color-blind female and a male with normal vision have three sons and six daughters. All the sons are color blind. Five of the daughters have normal vision, but one of them is color blind. The color-blind daughter is 16 years old, is short for her age, and has never undergone puberty. Propose an explanation for how this girl inherited her color blindness.

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