Excellent question. From this article:
With the “all-or-none” molecular nature of X-inactivation, a female heterozygote with an X-linked mutation has ~50% of her cells producing only the mutant X-linked gene product and ~50% of her cells producing only the wild-type product although “escape” can occur (see below). By contrast, every cell in a female heterozygote with an autosomal mutation transcribes both chromosome copies, such that each cell will have a 50% dose of wild-type gene product. Despite the fact that about half of the cells of X-linked heterozygotes express only the mutant gene, female heterozygotes of X-chromosome mutations can display reduced disease penetrance and/or severity compared with hemizygous males, indicating that the cells expressing the wild-type gene can provide protection against the disease.
If you need help interpreting this further, let me know!
Oh! So inactivation of one X chromosome happens independently in each cell of the organism and not in a coordinated manner in the whole organism, and so some cells might have the ill chromosome inactivated, while some others might have the wild one, resulting in the heterocygote always having a healthy chromosome working in many of the cells which grants a layer of protection against the illness.
That makes sense. Thank you very much!
Quick Reply
