I say inbreeding depression, you say heterosis

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We’ve talked a lot about inbreeding and the its health consequences many many times before ’round these parts. Most people think of the consequences in terms of unmasking recessive disorders like rare bith defects or the inability to feel pain. But the consequences are also apparent in complex traits–a new article shows a negative correlation between heterozygosity in the genome (inbreeding causes decreased heterozygosity) and both blood pressure and cholesterol levels.

These findings, if replicated, suggest that hR [heterozygosity] be considered as a genetic risk factor in genetic epidemiological studies on common disease traits. They are consistent with the well-known effects of heterosis (hybrid vigour) described when outcrossing animals and plants. Outbreeding resulting from urbanization and migration from traditional population subgroups may be leading to increasing hR and may have beneficial effects on a range of traits associated with human health and disease. Other traits, such as age at menarche, IQ and lifespan, which have been changing during the decades of urbanization, may also have been influenced by demographic factors.

4 Comments

  1. I wonder about the application of this idea to humans in general- give that the sampling was pretty restricted- to the Dalmatian islands in Croatia- especially since they are relating these processes to human demographic processes within the last 200K years. 
     
    I bet that the pattern would be completely different if they sampled throughout human diversity- especially African populations..

  2. I wonder about the application of this idea to humans in general- give that the sampling was pretty restricted- to the Dalmatian islands in Croatia- especially since they are relating these processes to human demographic processes within the last 200K years. 
     
    yeah, I agree, the conlcusions about demographic processes are pretty tentative. But for a given city in a country like, say, Croatia, you could imagine much mixing between people who previously lived in isolated villages coming together and the conclusions holding. The mixing of slightly inbred populations in an urban setting has been pretty well documented in Iceland (check out Reykjavik in figure 1). 
    http://www.nature.com/ng/journal/v37/n1/full/ng1492.html 
     
    On a larger scale (continental-scale migration), though, I’m not sure the conclusions would hold.

  3. Blood pressure and cholesterol levels? I don’t know about the disadvantages of a very low cholesterol level, but it seems genes that tend to raise your blood pressure are only disadvantageous in modern societies where you don’t have to worry about bleeding to death from an injury. Same with obesity and fat-storing genes. Anyone able to comment on this?

  4. it seems genes that tend to raise your blood pressure are only disadvantageous in modern societies where you don’t have to worry about bleeding to death from an injury. Same with obesity and fat-storing genes. Anyone able to comment on this? 
     
    sounds a lot like the ancestral succeptibility model for common disease.  
    http://www.gnxp.com/blog/2006/05/emerging-pattern-for-disadvantageous_14.php

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