An SSLP, which is a genetic locus of short nucleotide repeats, is on the X chrom

Question

An SSLP, which is a genetic locus of short nucleotide repeats, is on the X chromosome and located 2 map units away from the X-linked locus responsible for red-green color blindness. Three alleles of this SSLP locus are known: “4 repeats,” “5 repeats,” and “7 repeats.” A woman with normal color vision, but whose father is color blind, marries a man with normal vision, and they have a son.

Given the SSLP genotypes of the various family members shown above, what is the probability that the couple’s son is color blind?

Possible answers:

Family Member SSLP genotype Family Member SSLP genotype Woman's Father "5 repeats" Woman's Husband "3 repeats" Woman "5 repeats" / "7repeats" Couple's Child "5 repeats"

Explanation / Answer

The SSLP and the gene locus for color blindness are located 2 map units. From the given information, the chances of inheritance of the gene locus is 100%, since the gene for color blindness is maternally inherited by the son. The son shows the same 5" repeats as the mother, which further confirms.

Since the two regions are located 2 mu apart, the probability that the gene locus and the SSLP undergo recombination is 2%. Therefore, the chance that the given SSLP occurs as such, without recombination, along with the defective gene locus is 98%.

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