The David McWilliams genetic conundrum

strassenwolf

I was reading Mr McWilliams' column in today's Business Post - as usual, in my opinion, interesting stuff - and I came across the following comment, which jarred a little bit. It's obviously not a big thing, and may well have been a slip of the pen, but I'd be interested to get the views of the board.

David McWilliams wrote:

Some 20,000 feet below lie the Westman Islands, a great volcanic archipelago named after the Westmen - the Irish -who were taken here as slaves by the Vikings in the 10th century. This story explains why 30 per cent of Icelanders have Irish, not Norse genes. What’s more, considerably more Icelandic women than men have Irish genes, because the Vikings did what it said on the tin: they raped and pillaged, taking slave concubines home with them.

http://www.thepost.ie/post/pages/p/story.aspx-qqqt=DAVID+McWilliams-qqqs=commentandanalysis-qqqid=40624-qqqx=1.asp

I'm not quite sure what constitutes an Irish gene, but that's not really the point here. Let's assume there are such things.

There have been several generations since these slave concubines were relocated.

Assuming that these women were no different to other women around the world, they should - collectively - have produced approximately an equal number of sons as they did daughters. And those offspring would -collectively - have continued to do the same.

Given a 50:50 ratio of expressive genes from both the father and the mother in any union which produces offspring, one would imagine that these "Irish genes" should be approximately evenly divided between the sexes.

I hope the contributors on this board get what I'm trying to say. (I'm afraid this is my first post on the Biology and Medicine board).

My feeling is that unless these "Irish genes" - whatever they might be - are located on the sex chromosomes, a situation referred to by Mr McWilliams cannot be possible.

Am I correct?

darjeeling

strassenwolf wrote: »

I was reading Mr McWilliams' column in today's Business Post - as usual, in my opinion, interesting stuff - and I came across the following comment, which jarred a little bit. It's obviously not a big thing, and may well have been a slip of the pen, but I'd be interested to get the views of the board.



http://www.thepost.ie/post/pages/p/story.aspx-qqqt=DAVID+McWilliams-qqqs=commentandanalysis-qqqid=40624-qqqx=1.asp

I'm not quite sure what constitutes an Irish gene, but that's not really the point here. Let's assume there are such things.

There have been several generations since these slave concubines were relocated.

Assuming that these women were no different to other women around the world, they should - collectively - have produced approximately an equal number of sons as they did daughters. And those offspring would -collectively - have continued to do the same.

Given a 50:50 ratio of expressive genes from both the father and the mother in any union which produces offspring, one would imagine that these "Irish genes" should be approximately evenly divided between the sexes.

I hope the contributors on this board get what I'm trying to say. (I'm afraid this is my first post on the Biology and Medicine board).

My feeling is that unless these "Irish genes" - whatever they might be - are located on the sex chromosomes, a situation referred to by Mr McWilliams cannot be possible.

Am I correct?

I haven't seen the original research, but I'd reckon McWilliams' comments are based on a fairly hazy understanding of the actual biology.

I'd expect that if Icelandic pillagers had captured women from Ireland, you would see evidence of this in the modern mitochondrial DNA (mtDNA) pool. mtDNA (matrilineally inherited) of modern Icelanders would appear relatively similar to that of Irish people. The autosomal, nuclear DNA of Icelanders would be more similar to that of other modern people of Norse ancestry, with Icelanders' Y-chromosomes (patrilineal inheritance) looking even more Norse. My guess is that this is what has been seen, and that this is the basis of McWilliams' comments.

You might see more 'Irishness' on the X chromosome too, but geneticists tend to look at the mtDNA to get a clearer signal; the transmission of X chromosomes from fathers to daughters, and recombination between X chromosomes in mothers tends to blur things.

The comment that '30 per cent of Icelanders have Irish, not Norse genes' sounds equally vague. Without knowing the science on which it was based, it might mean that 30% of the Icelandic gene pool has a historical Irish origin, or that 30% of Icelanders have an Irish Y chromosome or mtDNA type.

darjeeling

Am J Hum Genet. 2000 Sep;67(3):697-717. (link here)

Estimating Scandinavian and Gaelic Ancestry in the Male Settlers of Iceland

Helgason A, Siguroardóttir S, Nicholson J, Sykes B, Hill EW, Bradley DG, Bosnes V, Gulcher JR, Ward R, Stefánsson K.

We present findings based on a study of Y-chromosome diallelic and microsatellite variation in 181 Icelanders, 233 Scandinavians, and 283 Gaels from Ireland and Scotland. All but one of the Icelandic Y chromosomes belong to haplogroup 1 (41.4%), haplogroup 2 (34.2%), or haplogroup 3 (23.8%). We present phylogenetic networks of Icelandic Y-chromosome variation, using haplotypes constructed from seven diallelic markers and eight microsatellite markers, and we propose two new clades. We also report, for the first time, the phylogenetic context of the microsatellite marker DYS385 in Europe. A comparison of haplotypes based on six diallelic loci and five microsatellite loci indicates that some Icelandic haplogroup-1 chromosomes are likely to have a Gaelic origin, whereas for most Icelandic haplogroup-2 and -3 chromosomes, a Scandinavian origin is probable. The data suggest that 20%-25% of Icelandic founding males had Gaelic ancestry, with the remainder having Norse ancestry. The closer relationship with the Scandinavian Y-chromosome pool is supported by the results of analyses of genetic distances and lineage sharing. These findings contrast with results based on mtDNA data, which indicate closer matrilineal links with populations of the British Isles. This supports the model, put forward by some historians, that the majority of females in the Icelandic founding population had Gaelic ancestry, whereas the majority of males had Scandinavian ancestry.

The paper above describes a study of Icelanders' Y chromosomes, and contrasts the results with earlier findings on their mtDNA. It sounds as though this work is the basis of McWilliams' comments on Iceland's genetic heritage.

Kevster

I was just about to say what the others have implied: That we'd need to know how the DNA of these subjects was measured. The Y chromosome accumulates few mutations over time and is passed on from father to son ONLY. This is the chromosome which is usually studied in population genetics or for mapping migrations of people (like the migration of people around the Meditterranean, for example).