GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2005-05 > 1117574358


From: "Andrew and Inge" <>
Subject: RE: [DNA] Middle Eastern ancestral markers on new Euro 1.0 test
Date: Tue, 31 May 2005 23:19:18 +0200
In-Reply-To: <REME20050531130221@alum.mit.edu>


-----Original Message-----
From: John Chandler [mailto:]
Sent: Tuesday, 31 May 2005 7:08 PM
To:
Subject: Re: [DNA] Middle Eastern ancestral markers on new Euro 1.0 test


Andrew wrote:
> That's how the maths works. Surnames die out too. It does not necessarily
> mean that people with a particular surname (say Li) have a greater
survival
> rate. It just has to do with how many children that have and how many of
> them are male. So it is just a probability thing.

I wrote:
> > That's true only of rare surnames and rare haplotypes.

Andrew replied:
> Not sure about that. Of course if it is just random loss of male lines
than
> more common surnames and haplotypes will take LONGER to die out.

Trust me. There is no conspiracy here. You mustn't confuse the two
juggernauts of rarity extinction and selective advantage. If there
are more males who survive from one surname or haplogroup than from
others, that surname or haplogroup has a selective advantage and will
"soon" come to dominate the population completely to the exclusion of
all others. (But note that the Y chromosome has so little function
that it offers small scope for a male-linked selective advantage.) On
the other hand, life is chancy, and there is a finite (and perhaps
even *large*) probability that the male line of any individual will
eventually end. This is the die-out tendency you're talking about,
and it's hard to beat, but there *is* a simple defence against it:
become common.

Here's the math. Suppose the probability of random individual
extinction is 99%. That's pretty daunting odds. However, the
extinction probability for a group is the Nth power of the individual
probability (where N is the size of the group). With even just a
thousand members, the group extinction probability goes down to
0.004%. Negligible.

Dear John

You say you'll show me the math, but then you don't, you only give the
results. How do you calculate an extinction probability, and what does the
term mean?

For example say a man, we'll call him Mr Jagger, has 5 sons and 5 daughters.
Suppose 2 of his sons have no children and the other 3 have 2 daughters
each. His 5 daughters all have 5 sons each. He now has 31 grandchildren and
his surname and Y DNA line are dead. To make it a little more realistic I
only need to add a few more random looking generations, as I'm sure you
realise. I can't see how you can say that this needs to imply anything at
all to do with selection.

Probabilites simply add up. If a single "nuclear" Y-family can die out so
can an extended one with thousands of male individuals. There is no need to
assume any selective advantage, and anyway selective advantage does not
apply only to pure Y chromosone inheritance as shown in my imaginary
example.

I don't have any references but I am aware of the fact, from reasing
something in the past, that a simple random computer programe which assumes
no selective advantage will show surnames or Y DNA dieing out even when they
have been in a majority situation.

Best Regards
Andrew






This thread: