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Effect of Inbreeding on IQ and Mental Retardation

N. E. Morton
Proceedings of the National Academy of Sciences of the United States of America
Vol. 75, No. 8 (Aug., 1978), pp. 3906-3908
Stable URL: http://www.jstor.org/stable/68793
Page Count: 3
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Effect of Inbreeding on IQ and Mental Retardation
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Abstract

Both decline of IQ and increase of mental retardation are consistent with rare recessive alleles at about 325 loci. There is no suggestion of a discrepancy that might be due to polygenic dominance or confounding of consanguinity with unfavorable environment. These data indicate that the risk for mental retardation in matings of normal parents increases from 0.012 with random mating to 0.062 for first-cousin parentage but that dominance deviations are a negligible cause of family resemblance of IQ. Implications for gene frequencies, mutation rates, and radiation response are detailed.

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