Can the lyon hypothesis be tested in a human female who is homozygous for one allele of the x-linked g6pd gene? why, or why not?

No, Presence of different alleles for an X-linked gene is required to test the Lyon hypothesis.

Explanation:

According to the Lyon hypothesis, to compensate the dosage of X linked genes in males and females of mammals, one X chromosome in all the cells of a female mammal is inactivated and the presence of the gene on the other X chromosome is expressed.

Inactivation of the X chromosome is a random process, that is, either maternal or paternal X chromosome may be inactivated during early embryological development in females.

To test the Lyon hypothesis, the expression of alternative alleles of an X-linked gene in the cells of a female mammal is studied. Given that the human female is homozygous for an X-linked gene, all of her cells would express the same allele for the gene, and the Lyon hypothesis can not be tested.