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Thread: Middle Eastern Populations Have Higher Recessive Disease Load

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    Middle Eastern Populations Have Higher Recessive Disease Load

    http://www.unz.com/gnxp/middle-easte...-disease-load/

    But a peculiar aspect of these dynamics is that when you look at runs of homozygosity in the genome, which usually measure more recent inbreeding, the Middle East and South Asia tends to have higher lower genetic diversity. To get a sense of South Asian populations, you can read The promise of disease gene discovery in South Asia. Because of caste/jati endogamy a lot of the South Asian groups have less genetic diversity than you might expect. This has disease implications.

    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).

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    This seems to be your proposal:

    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.

    -------------------------------------

    No evidence was presented for deleterious recessive alleles in this article.
    Genetic load is a term used here incorrectly. Homozygous recessive for sickle cell, for instance, die before reaching maturity. This is a load upon the population which is necessary, this recessive allele, since without this allele the heterozygous combination would not occur and it is this heterozygous individual who has resistance to malaria. The homozygous fatalities are the genetic load the population has to endure to achieve a balanced polymorphism allowing people to live in malarial areas.

    In fact, there is no problem whatsoever with homozygous recessives just so long as they are not harmful. There was no evidence presented for harmful homozygous recessives in this article. This article was written by some popular writer based on a scientific article they did not understand.

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    Quote Originally Posted by Shadow View Post
    This seems to be your proposal:

    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.

    -------------------------------------

    No evidence was presented for deleterious recessive alleles in this article.
    Genetic load is a term used here incorrectly. Homozygous recessive for sickle cell, for instance, die before reaching maturity. This is a load upon the population which is necessary, this recessive allele, since without this allele the heterozygous combination would not occur and it is this heterozygous individual who has resistance to malaria. The homozygous fatalities are the genetic load the population has to endure to achieve a balanced polymorphism allowing people to live in malarial areas.

    In fact, there is no problem whatsoever with homozygous recessives just so long as they are not harmful. There was no evidence presented for harmful homozygous recessives in this article. This article was written by some popular writer based on a scientific article they did not understand.
    It is true that homozygous recessives are not necessarily harmful, but absence of evidence isn't evidence of absence. For evidence of harmful effects of consanguinity in one Muslim population, please see:

    http://www.ncbi.nlm.nih.gov/pmc/arti...report=classic

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    Excessive consanguinity can lead to excessive pathologies: Tay Sachs among Jews being most important. This is why close incest is banned though for one generation it is harmless after all. Yet I still don't see why cousin marriage is so bad: the royals of Europe practice it with no serious costs. It's much rarer in European cultures but each to their own.

    Public opposition to cousin marriage is right wing nuts signalling against Moslems else liberal Americans signalling against rednecks.

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    Quote Originally Posted by Catterick View Post
    Excessive consanguinity can lead to excessive pathologies: Tay Sachs among Jews being most important. This is why close incest is banned though for one generation it is harmless after all. Yet I still don't see why cousin marriage is so bad: the royals of Europe practice it with no serious costs. It's much rarer in European cultures but each to their own.

    Public opposition to cousin marriage is right wing nuts signalling against Moslems else liberal Americans signalling against rednecks.
    And this is it, specific examples in a given breeding group. But to say homozygous recessives are harmful in the general and abstract is wrong.

    Let me give you an example. My Canadian Eskimo Dog comes from a highly inbred background. The Eskimos just didn't have that many dogs. The Eskimos did not practice selective breeding. They dogs just breed as wolves do with basically the same pack rules. But the Eskimos did practice culling. So dogs which did not come when called were shot. Dogs which did not work well or were distracted from work were shot. Weak dogs were shot. You get the picture.

    But Canadian Eskimo Dogs have absolutely no hip dysplasia. Hip dysplasia is a common condition found in most if not all dog breeds, especially large dogs. This is a homozygous recessive. To eliminate a homozygous recessive from the population is almost impossible yet it has been done here. And yet the population of Canadian Eskimo Dogs also called Inuit Dogs is highly inbred.

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