X chromosomes and Colorblindness - is there a way to distinguish certain mutations?

[Redmayne]

Is there a way to distinguish certain X chromosomes? Just like Y-DNA? What I am trying to say; is it possible to tell if an X chromosome is Celtic in origin or Amerindian in origin or Jewish in origin, etcetera. Is it possible to map certain areas where X chromosomes are found around the world?

This got me curious because I myself am somewhat colorblind. (Red-Green) And I recall reading a Jewish magazine that reported that 1 out of 4 or 5 Ashkenazi Jewish men are colorblind. (don't know the accuracy of that) But apparently; colorblindness comes from the X chromosome inherited from your mother; just like Mitochondrial DNA. Interesting right? I also heard that Jewish people tend to descend from about 4 mothers, and their most common mtdna is a homogeneously European mitochondrial K. (can anyone who is an expert give me some feedback? I find this to be very intriguing.) (

[geebee]

Is there a way to distinguish certain X chromosomes? Just like Y-DNA? What I am trying to say; is it possible to tell if an X chromosome is Celtic in origin or Amerindian in origin or Jewish in origin, etcetera. Is it possible to map certain areas where X chromosomes are found around the world?

This got me curious because I myself am somewhat colorblind. (Red-Green) And I recall reading a Jewish magazine that reported that 1 out of 4 or 5 Ashkenazi Jewish men are colorblind. (don't know the accuracy of that) But apparently; colorblindness comes from the X chromosome inherited from your mother; just like Mitochondrial DNA. Interesting right? I also heard that Jewish people tend to descend from about 4 mothers, and their most common mtdna is a homogeneously European mitochondrial K. (can anyone who is an expert give me some feedback? I find this to be very intriguing.) (

First of all, there are different kinds of color blindness or color deficiency. The most common, is generally called red-green color blindness or red-green color deficiency, and it's linked to a mutation or mutations in a gene on the X chromosome. Since a man lacks a second X chromosome -- which might be able to counter the effect of the copy with the mutation -- if he inherits this mutation he will be color deficient (like me) or color blind. A woman has two chances to inherit a "good" copy of the gene, and she will be color deficient or color blind only if she inherits the mutation from both parents.

There's also blue-yellow color blindness (or deficiency). This is associated with a mutation on chromosome 7, and so is not sex-linked. (It affects both sexes in more or less equal numbers.) There are also other types and causes of color blindness.

I don't know what the fraction is of Ashkenazi males who have red-green color blindness/deficiency. However, among "whites" generally, I believe it's something like one in eight -- so it's pretty common.

Unfortunately, one problem with tracking the X chromosome over a really long period of time via the use of haplogroups is that X chromosomes can recombine, just as the autosomes do. The chief difference is that everyone has two copies of each autosome -- doesn't matter whether you're male or female. So parents of both sexes can pass on recombined copies of their autosomes. Since only females have two copies of the X chromosome, however, they're the only ones whose X chromosomes can recombine.

Whether you're a son or a daughter, inherited an X chromosome from your mother that might be a recombination of the X chromosomes from both of your maternal grandparents. I say "might", because it's also possible that it could simply be a copy of your mother's maternal X or your mother's paternal X (with no DNA from the opposite grandparent). If you're a son, you won't have inherited an X chromosome from your father at all; you'll have inherited a Y chromosome. Only daughters inherit an X chromosome from each parent, and the one from their fathers are simply copies of the ones they inherited from their mothers.

There also is really only an incidental connection being the mtDNA and the X chromosome. Your mtDNA passed along just one path, no matter the distance involved. My mtDNA haplogroup is H1bg, and I can be fairly confident that if I follow my mother's mother's mother's (etc.) line back for 10 or 15 or 20 generations, the woman in that line will also be in H1bg. But it's doubtful that much -- if any -- of my X chromosome will trace to her. Only 20 cM of my X chromosome came from my mother's mother, with the rest being from my mother's father.

In fact, for two of my siblings there is no connection. That's because 100% of my brother's only X chromosome and 100% of my sister's maternal X chromosome came from our mother's father. So they didn't get an X chromosome from someone with the same mtDNA, except for our mother herself.

Of course, because endogamy among the Ashkenazi, it's likely that women on your other lines were also related to the women in your mtDNA line. So your mtDNA and your X chromosome are still separate, but it may be less likely that you'll be able to tell.

EDIT:

Also, while I believe you're right that K is the most common mtDNA haplogroup, there are a few others considered to belong to "founding mothers". Off the top of my head, I think it may be four. But if I remember correctly, they still only account for 40% of so of all mtDNA haplogroups found among the Ashkenazi. Somebody else can feel free to correct me ... and probably will.

[Redmayne]

Interesting insight.

You want to know something even more interesting? On the contrary to the Jews - I once read in a book - in the 1990s or so - that the Basque people of Spain were the ethnic group in Europe that had the LEAST amount of incidence of colorblindness. Only 1 out of 26 Basque men (if my memory serves correctly) had at least some form of Colorblindness. As contrary to the 1 in 4 (or 5) Ashkenazi Jewish men - I can't remember the exact numbers.)

This is often why I wondered if Colorblindness along with chromosomes/mtdna/Y-DNA may be (somehow) linked. (Or at least tell a story about a particular ethnic group and their genetic inheritance.)

I think the Polish scored second in terms of men least likely to be colorblind. (could this correlate with both Basque high frequencies of R1b (85%) and Polish high frequencies of R1a (57-62%)? In other words - these two populations are homogeneous and indeed show Y-chromosome homogeneity.


One thing strange about this theory - the Basques also tend to be a little more homogeneous on the female (mtdna) side. But the Polish women tend to be more hetereogenous. But, both populations tend to be homogeneous. (Most likely due to a founder effect and genetic isolation?)


I am wondering if this may be the reason why Jewish people are more likely to be color-blind than say Europeans and especially the aforementioned Basques and Polish. Maybe mitochondria doesn't have anything to do with it - but maybe (along with Y-DNA) it could map out how chromosomes (specifically X) affect the frequency of color-blindness. >>> Maybe it is because their Jewish female lineages tend to be more homogeneous than the paternal side. Get it? So maybe - the more a population is homogeneous on the female side; the more likelihood of the offspring being colorblindness. While to the contrary; the more homogeneous on the male side and more heterogeneous on the female side - the least likely the offspring may/are to be colorblind. See my point, here? Am I getting somewhere?


(Another oddity I found with the Basques and Polish (as well as other Slavic peoples) - were that Basques were highest in Rh- Type O Negative Blood - Meanwhile the Polish (and other Slavs) tended to have the least amount of Type O Negative among Europeans. Very strange, right?

I don't know where the Jews stand in this, unfortunately. (I do not know Jewish blood type frequencies.)

[geebee]

First of all, I really find the term "color blind" to be extremely annoying. Very few people are color blind. That condition is called achromatopsia and is the inability to perceive color at all. Those with this condition see in black and white and shades of gray.

It's also pretty rare -- affecting 1 in 30,000 worldwide, according to one source. https://ghr.nlm.nih.gov/condition/ac...sia#statistics

What most of the so-called "color blind" have is a color deficiency. This is usually caused by either the absence of one of the three photoreceptors, or -- more commonly -- by an abnormality in one of the them. For example, although some sources would lump me in with the "color blind", I am trichromatic just like most people. That is, I have three different photoreceptors. I'm not missing any of them.

Unfortunately, one of my photoreceptors does have an abnormality that makes it impossible for me to pass an Ishihara color plate test. I'm slightly "green weak". But, I can pass many other color vision tests, such as the D-15 color arrangement test and other color arrangement tests.

Anyway, it does seem that the Basques have a somewhat lower incidence of color deficiencies than northern Europeans: "4.02 percent in the males and 0.46 percent in the females" tested in one sample. https://www.ncbi.nlm.nih.gov/labs/articles/2378506/

However, the National Eye Institute (part of the National Institutes of Health) estimates that "As many as 8 percent of men and 0.5 percent of women with Northern European ancestry have the common form of red-green color blindness."
https://nei.nih.gov/health/color_blindness/facts_about

I also found one reference which reported a similar percentage for "New York Jewish boys and men", but it was from 1936. I have no idea how valid it is (or was). http://science.sciencemag.org/content/84/2175/228.1

One thing to consider is that the Ashkenazi have historically been very endogamous, which would result in a lot of people sharing large segments, even when they might not actually have been that closely related. This would be particularly true of the X chromosome, because people only have a fraction as many X-chromosome ancestors as they do autosomal ancestors.

On paper, everyone (potentially) has 32 3rd* great grandparents. (In reality, because of pedigree collapse the actual number is usually lower; sometimes much lower.) But a male only has a maximum of 8 3rd* great grandparents who could have contributed anything to his X chromosome.

And that's just the maximum. It could be less. For example, one of my brothers inherited an X chromosome from our mother that contains no DNA from our mother's mother. That is, my brother's single X chromosome only contains DNA from our mother's father. That, in turn, means it's all from our grandfather's mother. Going further back, how many of my brother's and my 3rd* great grandparents do you suppose could have made any contribution to my brother's X chromosome? Just 3. That's because

This has even greater implications for an endogamous group like the Ashkenazi, since a very small number of women might have passed on the same mutated genes to many descendants.

EDIT: *Corrected from 4th to 3rd great grandparents. The difference in the numbers gets even wider, though, as you go further back. On paper, you can have as many as 1,024 tenth great grandparents. But no more than 233 of these -- at most -- could be contributors to your X chromosome (if you're male; for females the number is 377).

By the time you get to twentieth great grandparents, on paper you could have over a million -- 1,048,576 to be exact. But only a little over ten thousand (10,048) of these could have contributed to your X chromosome. Again, this is for males only; for females, the number is higher. But still only a tiny fraction of the total number of twentieth great grandparents.