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View Full Version : Limits of selection against Neanderthal dna



Angela
15-01-19, 20:07
My take-away: there's been selection, just not the kind we thought.

See:

https://www.pnas.org/content/early/2019/01/14/1814338116

"SignificanceSince the discovery that all non-Africans inherit 2% of their genomes from Neandertal ancestors, there has been a great interest in understanding the fate and effects of introgressed Neandertal DNA in modern humans. A number of recent studies have claimed that there has been continuous selection against introgressed Neandertal DNA over the last 55,000 years. Here, we show that there has been no long-term genome-wide removal of Neandertal DNA, and that the previous result was due to incorrect assumptions about gene flow between African and non-African populations. Nevertheless, selection did occur following introgression, and its effect was strongest in regulatory regions, suggesting that Neandertals may have differed from humans more in their regulatory than in their protein-coding sequences.

AbstractSeveral studies have suggested that introgressed Neandertal DNA was subjected to negative selection in modern humans. A striking observation in support of this is an apparent monotonic decline in Neandertal ancestry observed in modern humans in Europe over the past 45,000 years. Here, we show that this decline is an artifact likely caused by gene flow between modern human populations, which is not taken into account by statistics previously used to estimate Neandertal ancestry. When we apply a statistic that avoids assumptions about modern human demography by taking advantage of two high-coverage Neandertal genomes, we find no evidence for a change in Neandertal ancestry in Europe over the past 45,000 years. We use whole-genome simulations of selection and introgression to investigate a wide range of model parameters and find that negative selection is not expected to cause a significant long-term decline in genome-wide Neandertal ancestry. Nevertheless, these models recapitulate previously observed signals of selection against Neandertal alleles, in particular the depletion of Neandertal ancestry in conserved genomic regions. Surprisingly, we find that this depletion is strongest in regulatory and conserved noncoding regions and in the most conserved portion of protein-coding sequences."

bicicleur
15-01-19, 20:53
Previous studies have found Basal Eurasian ancestry in all modern and some ancient Europeans [in this study, four ancient individuals show evidence of Basal Eurasian ancestry: Satsurblia (15 kya), Kotias (10 kya), Ranchot88 (10 kya), and Stuttgart (8 kya), SI Appendix, Fig. S6] (8, 19). Our finding that there is no ongoing decline in Neandertal ancestry in Europeans suggests that Neandertal ancestry in Europe has not been diluted in a significant way by gene flow from Basal Eurasians. Specifically, we find no difference in Neandertal ancestry in European individuals with and without Basal Eurasian ancestry (direct f4-ratio mean 2.31% vs. 2.38%, respectively; P = 0.36).

so, this is a mere coincidence :

https://1.bp.blogspot.com/-He8KH5HoUL4/V2SipopvDiI/AAAAAAAAFBY/KiqCB6AK6NIjQXFVoQ18ADphFo2N-PzjQCKgB/s1600/BE.png

Those on the right hand side of this graph are not the ones nearest to Africa, they are the nearest to Dzudzuana cave.

Is there a list of the European individuals in this study?

bicicleur
17-01-19, 11:04
I think 2 seperate phenomenon are acting : selection and dilution.
It is logic that selection only acts on genes and not at random DNA.
But there is also dilution. And I don't think it came from Africa, but from Basal Eurasian, in spite of what the authors of this study claim.
Is there a list of the European individuals in this study? With their share of BE and Neanderthal admixture?