6. Male-limited precocious puberty results from a rare, sex limited autosomal al

Question

6. Male-limited precocious puberty results from a rare, sex limited autosomal allele (P) that is dominant over the allele for normal puberty (p) and is expressed only in males. Bill underwent precocious puberty, but his brother Jack and his sister Beth underwent puberty at the usual time, between the ages of 10 and 14. Although Bill's mother and father underwent normal puberty, two of his maternal uncles (his mother's brothers) underwent precocious puberty. All of Bill's grandparents underwent normal puberty. Give the most likely genotypes for all the relatives mentioned in this family 7. In goats, a beard is produced by an autosomal allele that is dominant in males and recessive in females. We'll use the symbol B for the beard allele and B for the beardless allele. Another independently assorting autosomal allele that produces a black coat (W) is dominant over the allele for white coat (w). Give the phenotypes and their expected proportions for the following crosses a. B Bb Ww male x BB Ww female b. B BbWw male x B Bww female c . B. B'Ww male × B"B"Wiv female d. B.BbWw male × B"Bbww female

Explanation / Answer

It is given that P is dominant over p

Only a condition with pp will cause the precocious puberty.

Given that Bill is pp, and his parents were normal. His sister and brothers are normal.

To get a child homozygous recessive it is mandatory that both of the parents of Bill were Pp that is heterozygous normal.

But maternal uncles were gone through precocious puberty so they will be pp.

It means that her maternal grandparents were either Pp.

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