h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Plymouth Exile,

I realise my mistake; I didn't quite understand the difference between haplotype and haplogroup.
So what I should have said is that I get the impression a given individual can have have more than one haplotype, because a DNA test only analyses a particular section of the DNA, rather than the whole non-recombining section.

In this case, 50% of those Irishmen tested might have a particular haplotype variant on another section of their DNA, which would seem to indicate that randomn mutations can result in a coincidentally similar pattern.

Einion,

As far as I am aware, from what I have read, the whole of the non-recombining part of the Y-Chromosome is analysed in population DNA testing. The very fact that this part is non-recombining means that it passes from father to son unchanged, so there is no possibility that a sequence similarity could come about by chance. Thus by examining the non-recombining part of a man’s Y-Chromosome, one is effectively examining the non-recombining part of the Y-Chromosome of his direct male line ancestors over the time period of a hundred or more generations.

An individual man has only one Haplotype in the non-recombining part of his Y-Chromosome. Only 95% of the Y-Chromosome, and the mitochondrial DNA (mtDNA) are non-recombining. All other sections of DNA are recombining, and therefore do not pass from father to son (or from mother to daughter in the case of mtDNA) unchanged, so the Haplotypes of these parts are of no use in population genetics studies. Haplotypes of the Y-Chromosome do not occur in other parts of the DNA, and vice versa.

Population genetics studies only tell us about the direct male ancestral line (Y-Chromosomes) and the direct female ancestral line (mtDNA), and nothing at all about the many other ancestral lines. However, if 98% of the men in a region of Western Ireland have Y-Haplotypes which fall into a single Haplogroup (R1b), by virtue of being related Haplotypes, then it is statistically extremely probable that somewhere in the region of 98% of the males in the same locality a thousand years ago had Y-Chromosome Haplotypes in the R1b Haplogroup.

"The very fact that this part is non-recombining means that it passes from father to son unchanged, so there is no possibility that a sequence similarity could come about by chance."

Plymouth Exile,

Randomn mutations are of course what enable scientists to trace common descent, so the Y-chromosome is sometimes passed from father to son unchanged, but sometimes with a new mutation (otherwise there'd be no variation in Y-chromosomes).
So I'm saying that theoretically there is a chance that the same mutation on the same locus could occur in unrelated lineages.

But having thought more on the subject, and seen some maps, it appears that the chance of such a coincidence is so low as to be practically impossible.

Ozzie Exile,

It's often not possible to tell where someone comes from, however I have certainly seen Danes and Germans who can easily be distinguished from English or Irishmen by their physical appearance alone. Others are of course, more difficult to "spot".

But a lot of people can often tell someone's nationality by physical appearance; to some extent culture and mentality can affect someone's look, but quite often it's even possible to guess that an Australian is of Irish or of Welsh descent, due to subtle differences. It depends largely on how familiar one is with a given nationality.


As I mentioned in my third last post, the Romans noted differences in physical appearance between the usual Celts and certain tribes in Britain.

>>Some of these large-scale studies (such as the whole of Europe) seem to lack detail. I can't remember a specific instance so I'll give a hypothetical example: let's say 98% of the Irish have the RB1 Haplogroup, but then 50% have some other haplogroup. I'm pretty sure I've seen similar apparent contradictions.<<

Plymouth Exile,

I think my confusion here arose from the fact that some surveys are talking about sub-haplogroups. Added to this, the names of particular haplogroups aren't always the same. There is more than one naming system.

So 98% of men in a district might be R1B, and 50% might be of a sub-haplogroup within R1B, but, as you say, those 98% percent are still descended from a common ancestor.

Einion,

You are quite right about the confusingly different Y-Chromosome Haplogroup naming systems. I recently found the following link, which equates the different names:-

http://ycc.biosci.arizona.edu/nomenclature_system/fig1.html

You are also correct in stating that while 98% of the men in a district may be of Haplogroup R1b, there are a number of sub-Haplogroups within R1b, and these men could be from a number of these sub-groups, adding up to a total of 98%.

Thanks for the link. That should be helpful.

Hello. I am a descendant of Lambles from Devon and have traced my line back to 1550. Would you like to see if we share ancestors?

My mother's maiden name was Lamble.