Archiver > GENEALOGY-DNA > 2010-11 > 1289788430

From: Kathy Johnston <>
Subject: Re: [DNA] Heterozygosity on the X.
Date: Sun, 14 Nov 2010 21:33:50 -0500

[DNA] Heterozygosity on the X.
John, what do you mean by heterozygosity once per 3 scroll jumps? I assume each time you scroll, a page of results changes.
What % of the total markers are heterozygous in the non-crossing part of the X for males?

FF at FTDNA has not changed, but 23andMe has changed their reporting to no-calls for heterozygous results and I do see some males who have a lot of no-calls. One male I know has 268 no-calls on the X in an area that is normally non-recombinant for males. This male has only tested his autosomes at 23andMe. I don't know what he would be in Family Finder. I wish I knew what this meant.

If you accept the possibility that Thomas Krahn is right and there really are no NRY (non-recombinant Y chromosomes), maybe there are more than the average number of SNPs on the Y chromosome that have accepted alleles from the X. The male I know has a rather unusual appearing Y based on unusual STR numbers, so maybe there are some SNPs that have been repaired by an ancestor's X causing false positives when the X is probed, hence heterozygosity. This may be a rare observation so that is why it has not been reported. We can't tell because this male has not been subjected to advanced SNP testing for the Y. Does your male have an unusual Y? You can answer me off list to avoid privacy issues.

Anybody who is a project administrator who runs across a male with two Xs should probably know about Klinefelter's syndrome. It does not sound like that is the problem in your male's case unless you are talking about a very high number of heterozygous results.

Kathy J.

> I know that they report 2 values for the X chromosome even if the person
> is a male. However, does anyone know what the incidence of seeming
> heterozygosity for a male in the non-crossing part of the chromosome is?
> That is: I have a male on FTDNA who has apparent heterozygosity on an
> allele about once per 3 scroll jumps. Are those no calls?

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