a. A male mouse that is heterozygous for a reciprocal translocationbetween the X

Question

a. A male mouse that is heterozygous for a reciprocal translocationbetween the X chromosome and an autosome is crossed to a femalemouse with a normal karyotype.

The autosome involved in the translocation carries a generesponsible for coloration of the fur. The allele on the male'stranslocated autosome is wild-type, and the allele on itsnon-translocated autosome is mutant; however, because the wild-typeallele is dominant to the mutant allele, the males fur is wild-type(dark in color). The female mouse has light color in her furbecause she is homozygous for the mutant allele of thecolor-determining gene.

When the offspring of the cross are examined, all the males havelight fur and all the females have patches of light and dark fur.Explain these peculiar results.

Explanation / Answer

answer :

1.The phenotype in the femaleoffspring is mosaic because one of the X chromosomes is inactivatedin each of their cells.

2.If the translocated X isinactivated, the autosome attached to it could also be partiallyinactivated by a spreading of the inactivation process across thetranslocation breakpoint.

3.This spreading could thereforeinactivate the color-determining gene on the translocated autosomeand cause patches of tissue to be phenotypicallymutant.

all above explanation is based onLyon's hypothesis .

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