A gene for a recessive genetic disease (st) in gerbils is linked to an RFLP. A f

Question

A gene for a recessive genetic disease (st) in gerbils is linked to an RFLP. A female from a pure-bred strain of gerbils unaffected by the disease is crossed to a male from a pure bred strain affected by the disease. The F1 were crossed to produce an F2 that Included eight pups, as shown in the pedigree below and Southern blot below. Each column in the Southern blot correspond to the individual above It in the pedigree. The genotype of individual III-6 is 7kb st / 7kb st 4kb ST / 4kb ST 4kb st/ 4kb st 4kb ST / 7kb SST 4kb ST / 7kb st

Explanation / Answer

The answer is C.

The disease is an autosomal recessive inherited disorder. In F2 generation, the III-6 is affected by the disease as it received the two copies of the recessive alleles (st).   The genotype of individual III-6 is 4kb st/4kb st, because it is linked to an RFLP, the RFLP pattern for the recessive allele is 4 kb. Hence only one band near 4 kb is found and is homozygous recessive alleles.

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