A rare form of polydactyly (extra fingers and toes) in humans is due to an X-lin

Question

A rare form of polydactyly (extra fingers and toes) in humans is due to an X-linked recessive gene. The chromosomal location of this gene is unknown. Suppose a geneticist studies a family with the following pedigree. She isolates DNA from each member of this family and analyzes these samples by Southern blotting, using a probe that consists of a cloned DNA sequence from the X chromosome. Results from this analysis are shown below.

a. For each person in the pedigree, give his or her genotype based on RFLPs revealed by the probe. Your genotypes should clearly indicate which individuals share common alleles based on the RFLP patterns.

b. Is there evidence for close linkage between the probe sequence and the X-linked gene for polydactyly? Why or why not?

c. How many of the daughters in the pedigree are likely to be carriers of X-linked polydactyly? Why?

Explanation / Answer

1. In the pedigree given, the probe shows three different alleles A allele : high band, B allele: twi intermediate bands C allele: two low bands and one intermediate band.

Female: AB, Male: CY, Offspring : AY, BY, BC, BY, AC, BY, AY

2. Three male offspring having allele 'B' has polydactyly while those donot have have B allele donot have polydactyly.

3. One female offspring contain 'B' allele so she will be carrier of polydactyly.

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