GENETICS Polydactyly is an autosomal dominant trait (the alleles for this gene a

Question

GENETICS

Polydactyly is an autosomal dominant trait (the alleles for this gene are P and p). Cataract formation (an eye disorder that can lead to loss of vision) is also an autosomal dominant trait (the alleles for this gene are C and c). The genes for these traits are found on chromosome 18 and are tightly linked. A man suffers from both of these traits and is found to have the genotype P c/ p C. If his wife is phenotypically normal, the man’s first child is most likely to have:

A) either polydactyly or cataracts

B) both polydactyly and cataracts

C) neither trait

Explanation / Answer

A) either polydactyly or cataracts

Since the genes aer completely linked, the gametes produced by man with the genotype P c/p C are Pc and pC, which is similar to parental genotype (because no recombination during meiosis occurs). The femae is normal, means the genotype is ppcc and the gametes produced will be pc and pc.

Now the genotypes of resulting offspring will be, Ppcc, Ppcc, ppcC, ppcC. As the traits for polydactyly and cataractsare autosomal dominant, the first child will have either polydactyly or cataracts.

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