Male-limited precocious puberty results from a rare, sex-limited autosomal allel

Question

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 undergoes 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, his two maternal uncles (his mother's brothers) underwent precocious puberty. All of Bill's grandparents underwent normal puberty. Match the most likely genotypes for a relative in his family below. if there is an equal likelihood of multiple genotype for relative, place each possible genotype.

Explanation / Answer

Bill - Pp

Jack - pp

Beth- Pp or pp

Father - pp

Mother - Pp

Uncle - Pp

Grand father - pp

Grand mother -

Precocious puberty is said to be dominant and hence all the males who experienced normal puberty (Jack, Bill’s father, and Bill’s grandfathers )must be pp. Bill and his maternal uncles, who all experienced precocious puberty, are Pp. They are expected to be heterozygous because P is a rare allele and also these individuals all had fathers that are pp. Hence Bill could have inherited P only from his mother, who should have been Pp. Bill’s sister Beth can be either Pp or pp.

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