**update 08/03: post fixed to remove references to roh which i got wrong (roh≠blocks of ibd!) — see comments below (thanks, citrus!)**
princenuadha points me to this awesome pdf which i guess was a presentation given at a society for molecular biology and evolution (smbe) conference last weekend (thanks, prince!).
here is an interesting graphic from the presentation (pg. 21):
what this map shows are the means of
runs of homozygosity (remember those?) blocks of identity by descent (ibd) that are greater than 1cM for each of these european populations. the longer the ibd blocks, the greater the identity by descent, and vice versa. small circles=fewer long blocks of ibd; large circles=more long blocks of ibd.
if a population has lots of short blocks of ibd, then its genetics are all mixed up, possibly due to outbreeding or because of a fairly recent mixing with another population. if a population has lots of long blocks of ibd, then its genetics are not so mixed up and the individuals within it share a lot of identity by descent. this can be an indicator of having been squeezed through a bottleneck or close inbreeding over time.
here are the mean numbers of long blocks of ibd for some of the countries on the map:
as you can see, my “core europeans” (english, french, germans, dutch, prolly some others) all have low means of blocks of ibd. the smallest circles are found right in the center of nw europe: england, france, belgium, germany. also italy (more about that below). in the immediate periphery around core europe, the circles are a bit larger, i.e. there are more long blocks of ibd: scotland, ireland, spain, portugal, switzerland, greece, scandinavians. eastern europeans have even larger circles/even more long blocks of ibd: poles, russians. and populations in the balkans, like the albanians, have enormous circles, i.e. LOTS of long blocks of ibd.
all of that fits the pattern i’ve been talking about here on the ol’ blog (see the mating patterns series below in the left-hand column): that the core europeans have been outbreeding the most and for the longest, with peripheral europeans lagging behind that trend, and eastern europeans really lagging behind the trend. i haven’t actually discussed the balkan populations (yet), but i do know that cousin/endogamous marriage rates are pretty high in the balkans.
i wonder if the numbers for italy may be unrepresentatively low, but it’s difficult to know. the data used are from popres and, like so much genetic data out there, have no provenance info attached to them. so, are the italian data from northern italy (which has a long history of outbreeding) or southern italy (which has a lot of inbreeding) or a combination of both? dunno.
this is a very cool study! i like it a lot. (^_^)
polish gen also has an interesting post about the presentation, btw.
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