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May 15, 2004

Genetically determined, but not really "heritable"

In the comments for an earlier post I pointed to this page which elaborates on the concept of narrow sense heritability, that is, the (additive genetic variance)/(phenotypic variance) (remember, exclude dominance effects since they are obviously not "additive"). That brings me to a point that might need some repeating: a trait can be genetic, but not particularly heritable. From the site linked to above: Consider a trait like reproduction. The development and ovulation of an egg, implantation and support of an embryo, and development of the placenta are well-orchestrated biological events controlled by genes. However, most heritability estimates for reproductive traits are low. Why would heritability be low for reproduction? Well, obviously the fitness cost for having a reduced capacity for reproduction (infertility as the extreme case) is pretty high, so humans all basically have a capacity to reproduce, and there isn't much variation in the phenotype that is due to genetic variation (directly at least). If you want a feel for heritability estimates across phenotypes, check out this site, which deals with domesticated animals (heritability is important in this context because of selective breeding).

Posted by razib at 10:56 PM