Thursday, August 18, 2016

inbred, genetically-defective, racist atavisms...?

unz |  Middle Eastern, North African, and Pakistani populations are even more extreme. You can see it in the figure above. Across short runs of homozogosity the results converge onto what you’d expect, roughly. But Middle Eastern populations are a huge anomaly at long runs. That’s because of this:
From 20–50% of all marriages in the GME are consanguineous (as compared with 0.2% in the Americas and Western Europe)1, 2, 3, with the majority between first cousins. This roughly 100-fold higher rate of consanguinity has correlated with roughly a doubling of the rate of recessive Mendelian disease19, 20. European, African, and East Asian 1000 Genomes Project populations all had medians for the estimated inbreeding coefficient (F) of ~0.005, whereas GME F values ranged from 0.059 to 0.098, with high variance within each population (Fig. 2c). Thus, measured F values were approximately 10- to 20-fold higher in GME populations, reflecting the shared genomic blocks common to all human populations. F values were dominated by structure from the immediate family rather than historical or population-wide data trends (Supplementary Fig. 8). Examination of the larger set of 1,794 exomes that included many parent–child trios also showed an overwhelming influence of structure from the immediate family, with offspring from first-cousin marriages displaying higher F values than those from non-consanguineous marriages (Fig. 2d).
For me this was the most interesting, and sad, result:
Despite millennia of elevated rates of consanguinity in the GME, we detected no evidence for purging of recessive alleles.Instead, we detected large, rare homozygous blocks, distinct from the small homozygous blocks found in other populations, supporting the occurrence of recent consanguineous matings and allowing the identification of genes harboring putatively high-impact homozygous variants in healthy humans from this population. Applying the GME Variome to future sequencing projects for subjects originating from the GME could aid in the identification of causative genes with recessive variants across all classes of disease. The GME Variome is a publicly accessible resource that will facilitate a broad range of genomic studies in the GME and globally.
The theory is simple. If you have inbreeding, you bring together deleterious recessive alleles, and so they get exposed to selection. In this way you can purge the segregating genetic load. It works with plants. But humans, and complex animals in general, are not plants. More precisely the authors “compared the distributions of derived allele frequencies (DAFs) in GME and 1000 Genomes Project populations.” If the load was being purged the frequency of deleterious alleles should be lower in the inbreeding populations. It wasn’t.
Middle Easterners should stop marrying cousins to reduce the disease load.