Question

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?

Short answer

Why or why not? Answer: No, the Lyon hypothesis cannot be tested in a human female who is homozygous for one allele of the X-linked G6PD gene. This is because both X chromosomes carry the same gene copy, so even if X-inactivation occurs, it would not lead to any observable differences in gene expression in this specific situation.

Step-by-step solution

Understanding X-inactivation (Lyon hypothesis)

X-inactivation is a process in which one of the two X chromosomes in female mammals is randomly inactivated to achieve gene dosage compensation. This is important because males only have one X chromosome, so if females expressed genes from both of their X chromosomes, they could end up with twice the amount of X-linked gene product, which might lead to an imbalance between different gene products. The Lyon hypothesis proposes that this random X-inactivation occurs early in development, and the inactivated X chromosome forms a compact structure called a Barr body.

Knowing the role of G6PD gene

The G6PD gene is an X-linked gene that encodes an enzyme called glucose-6-phosphate dehydrogenase, which plays an essential role in red blood cell metabolism. Homozygous refers to a situation when an organism possesses two identical copies of a particular allele. So a female Homo sapiens who is homozygous for one allele of the X-linked G6PD gene would have the same G6PD gene variant on both of her X chromosomes.

Testing the Lyon hypothesis in a G6PD homozygous female human

To investigate Lyon hypothesis, it is necessary to examine whether both X chromosomes are active or if one of them is inactivated, leading to a gene dosage balance. In a female human who is heterozygous for the X-linked G6PD gene (carrying two different alleles), cell populations would express different alleles due to random X-inactivation, making it possible to test the Lyon hypothesis. However, in a female human who is homozygous for one allele of the X-linked G6PD gene, there would be no difference in gene expression between the cells where the first X chromosome is inactivated and those where the second X chromosome is inactivated. Both copies of the gene are the same, so even if X-inactivation occurs, it would not lead to any observable differences in gene expression, making it impossible to test Lyon hypothesis in such cases. In summary, the Lyon hypothesis cannot be tested in a human female who is homozygous for one allele of the X-linked G6PD gene because both X chromosomes carry the same gene copy, so X-inactivation will not lead to any observable differences in gene expression in this specific situation.