Anonymous asked:

you said in your post about color blindness that the first two are more common in men is there a reason for that or..? I'm curious

tobeagenius answered:

(Anon is referring to this post) Yes there is a reason! Red-Green colour blindness has two subtypes; deuteranomalia and protanopia. Both of which are significantly more common in men, and this is all to do with genetics and how it is inherited.

We all have 23 pairs of chromosomes, half from each parent. You’ll notice, however the 23rd pair differs from the rest. This is beacause it determines whether the individual is male or female, so it is called the sex chromosome. Females have XX and males have XY. 

You’ll notice the X chromosome is much larger than the Y chromosome and this is because in addition to carrying genes that determine sex, it also carries genes that code for non-sexual characteristics, including that for red-green colour blindness. Okay so now I’m going to assume you have a vague understanding of what a recessive/dominant allele is, if not, this page gives a pretty good explanation. 

I’ve made a quick graphic to sum up the next part because it can be a bit confusing:

Crucially, the gene that causes red-green colour blindness (shown in red) is recessive, so females need two copies of the gene to express the trait & be colour blind. The probability of this is low because if a female has a dominant allele on her other X chromosome (white), that will be expressed instead and she will have full colour vision. For this reason, red-green colour blindness is not very common in women (present in less than 0.5% of white women).

However, since men have the XY chromosome pair and not XX like females, if they have the colour blind gene on their only X chromosome, it will be expressed anyway. There is no corresponding dominant allele to override it. As a result, it is much more likely for a male to be colour blind (seen in 6-8% of white males).

This explanation became a hell of a lot longer than I expected but I hope this makes sense, genetics can be confusing af so I tried to break it down as much as possible. Other X linked traits include haemophilia (where blood can’t clot properly), and baldness.