GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2007-07 > 1184606158


From: James Heald <>
Subject: Re: [DNA] Do Haplogroups change after death?
Date: Mon, 16 Jul 2007 18:15:58 +0100
References: <008701c7b415$794b0120$2401a8c0@your447023ae6b> <REME20070705181857@alum.mit.edu> <a81622ac0707051724y16754956obfb853b6686e74ed@mail.gmail.com> <REME20070707152459@alum.mit.edu> <a81622ac0707071304x11373a0en3b0b4e52a7b2e3c@mail.gmail.com> <REME20070707183721@alum.mit.edu> <a81622ac0707071637o34a3421dr36660529da9f75a4@mail.gmail.com> <REME20070709202718@alum.mit.edu> <a81622ac0707092003u290a5dd4s96c4a87a62fe3230@mail.gmail.com> <REME20070711175004@alum.mit.edu> <a81622ac0707120434g62d3796bk63d9ce33299bb67c@mail.gmail.com> <REME20070713160416@alum.mit.edu><7.0.1.0.2.20070715011550.02457910@netvision.net.il>
In-Reply-To: <7.0.1.0.2.20070715011550.02457910@netvision.net.il>


yair wrote:
> To James Heald or anyone else who can answer the question at hand
> (and not bring up other matters):
> Is anything wrong with the statement below:
>
> Haplotypes are determined by STRs which are considered relatively
> volatile whereas haplogroups are determined by SNPs which are
> considered stable.

Vince has given a clearer statement, but yeah, as applied to normal
father -> son transmission, that's not too misleading.

> It is admitted that haplogroups may change from one classification to
> another AFTER DEATH due to what is termed "Degrading" or "deterioration".
> The explanation is that while the organism lives a defence mechanism
> maintains that haplogroup as it is.
> After death the defence mechanism is removed and changes can take place.
> it would therefore appear that SNPs are not necessarily as stable as
> all that and hypothetically at least external influences could
> conceivably have the same effect on a living organism.

To add to what others have said:

The whole body is going to deteriorate after death. But where
scientists /have/ been able to extract the relevant DNA from bones, I
think they're fairly confident about what they've found.

To start with, they're extracting lots and lots of cells. So even if
one Y chromosome had taken eg a precise chemical or cosmic ray hit, most
would not be mutated.

Secondly, as somebody said, the degradation is mostly the chromosomes
falling apart completely - not specific mutations. So if the DNA can
be extracted at all, it is likely that either no consistent data
emerges, or the overwhelming number of copies are consistent with the
original.

Thirdly, as somebody else pointed out, it's wildly unlikely that a SNP
change would be of exactly the kind that is believed to have occured
naturally once in the whole of human history. And a post-mortem
environmental STR change is even less imaginable, without the whole
strand of DNA having fallen apart.

Finally, note that in vivo mutations are most likely to occur in strands
of DNA which have been unzipped for reading or for replication. Neither
of those processes are going on post mortem.

So if researchers are getting a clear unambiguous signal from the bones
of St Luke, it's likely to be correct. But if degradation has occurred,
they won't be getting a clear unambiguous signal.


If you really want to question these results, a more productive line
would be to ask about possible contamination from contemporary sources
of DNA (eg the researchers' own DNA). Remember O.J. (!) But this is a
now well-recognised issue, that people are now well aware of, and I
would believe that quite strict protocols to prevent it are likely to be
in place.

All best,

James.


This thread: