Why can the lyon hypothesis not be tested in a human female who is homozygous for one allele of the x-linked g6pd genea. one cannot test the lyon hypothesis in a human female with homozygous x-linked genes because the test requires an individual with an abnormal set of chromosomes (47, xxx or 48, ) to see differences in x chromosome activity. b. one cannot test the lyon hypothesis in a human female because inactivation of x chromosome occurs early in embryonic development. c. one cannot test the lyon hypothesis with homozygous x-linked genes because in the absence of allelic alternatives inactivation of x chromosome does not occur. d. one cannot test the lyon hypothesis with homozygous x-linked genes because the test requires identification of allelic alternatives to see differences in x chromosome activity.

D. One cannot test the Lyon hypothesis with homozygous X-linked genes because the test requires identification of allelic alternatives to see differences in X chromosome activity.

Explanation:

Lyon hypothesis explains dosage compensation in mammals with XX-XY type of sex determination. The human females have two copies of X chromosomes while human males have only one copy of the X chromosome.

To balance the number of X linked genes between males and females, one X chromosome in all the somatic cells of a human female is inactivated during early embryonic development and is a presence in form of Barr body.

The inactivation of the X chromosome is random and either maternal or paternal X chromosome from a cell of a human female can be inactivated.

To observe the Lyon hypothesis, the expression of X linked genes is observed. For the purpose, the female should be heterozygous for a particular X linked gene to observe the expression of different alleles in her cells due to random inactivation of either of the X chromosome.

A human female with a homozygous X linked gene would express the same allele of the gene in all of her cells irrespective of the inactivation of the paternal or maternal X chromosome.