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From: Vincent Vizachero <>
Subject: Re: [DNA] Questions about alternate means of searching DNA Genealogy
Date: Wed, 31 Mar 2010 05:10:24 -0400
References: <209bca921003291224k5f0b3ae2gef0ece518f0327f1@mail.gmail.com> <REME20100329212910@alum.mit.edu><000001cacfe2$817a39b0$846ead10$@com><REME20100330160616@alum.mit.edu><000001cad0ac$a0be9f80$e23bde80$@com>
In-Reply-To: <000001cad0ac$a0be9f80$e23bde80$@com>


No, not in the context of the Y-chromosome.

As John said, the Y does not split and recombine: it is handed down
pretty much identically from father to son. If a father has two rare
alleles, his son will almost surely have the same two rare alleles.

Autosomal DNA does recombine, so you can assume that allele
frequencies are somewhat independent. But in Y-DNA, you can't assume
it: you'd have to investigate it. It becomes an empirical question,
not a theoretical one.

Take an example in haplogroup R1b1b2. DYS393=12 is fairly rare, and
DYS426=11 is fairly rare. However, those two alleles tend to co-
occur: nearly half the people with DYS426=11 also have DYS393=12.

In the R1b project at FTDNA, DYS393=12 is about 5.4% of the project.
DYS426=11 is about 1.7% of the project. You might assume the joint
probability is 5.4%*1.7%=0.09%, but you'd be wrong. The joint
probability is actually 0.7%, nearly eight times greater.

VV



On Mar 31, 2010, at 4:31 AM, Sandy Paterson wrote:

> Surely, if we examined the haplotypes of the sons of a large number
> of men
> with two rare alleles, although we'd find that in most cases sons
> would have
> both rare values, we'd also find that some sons would have only 1? And
> (albeit very rarely), some brothers would have none?


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