Comment on It do be like that
ornery_chemist@mander.xyz 1 year agoThis is not true. That women cannot have the congenital dichromacy (or anomalous trichromacy) that biological males commonly have is flat out wrong. A biological female can still be a protan or deutan, but the phenotype requires that both X chromosomes carry the recessive color vision-deficient alleles. Nevertheless, given that ~8% of all X chromosomes have such a gene regardless of sex, the incidence in the female population is still around half a percent, which is not insignificant.
Interestingly, one form of tetrachromacy in females actually has the same cause of color vision deficiency in some males (specifically anomalous trichromacy). From what I understand, only one X chromosome is active per cone cell, and which one is active is random. So, half of such a person’s cone cells of one type are “normal” while the rest of that type are anomalous and have a slightly different peak wavelength. The net result is four different types of cone cells, i.e., tetrachromacy, which may have an incidence of more than 10% in females.
sndrtj@feddit.nl 1 year ago
X-inactivation is a little bit more complicated than that. While the process of X-inactivation initiation is random, once a cell has settled on one chromosome, all its daughter cells will silence the same chromosome. The initial process happens in the early embryo, so large patches of the body have the same X chromosome silenced.
This pattern is visible in some animals. E.g. a tortoise cat’s pattern arises due to the hair color gene existing on the X chromosome. Consequently, male tortoise cats are rare (XXY, XXXY etc only)
ornery_chemist@mander.xyz 1 year ago
Neat, thanks for the clarification. Even though the initial proportion is 50/50 for X-activation, are there scenarios where one daughter line is more prominent than the other, or does it usually remain 50/50?
sndrtj@feddit.nl 1 year ago
Statistics would indicate that that is a plausible scenario.
In addition, a uniparental disomy can occur as well. Here, the X chromosome was duplicated in the egg cell. So the exact same X chromosome is inherited twice.This is an error in meiosis. This could occur in XXX (with the third X from the father’s side), XXY, or even XX. That latter one would be rare, for a uniparental disomy on X without a third sex chromosome would mean both egg and sperm cell had an error during meiosis.
You could also see a single X (Turner Syndrome) as a 100% dominant X-chromosome. But that may be semantics.