The Load of Lethal Mutations in White and Negro Brazilian Populations II. Second Survey

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Abstract
Data obtained in the Brazilian State of Minas Gerais confirmed previous findings that "premature" mortality (i. e., mortality from the first weeks of pregnancy to the age of about 20) is very little increased in the offspring of consanguineous marriages among whites (of Portuguese ancestry), but substantially increased among Mulattoes and Negroes. This fact is probably due to whites having a small load of detrimental mutations of the kind responsible for the inbreeding effect (perhaps less than 1 lethal equivalent per person) while Negroes probably present a rather heavy load (around 10 lethal equivalents per person). Some hypotheses for explaining these findings have been discussed. It is suggested that mortality due to the lethal equivalents here revealed may be roughly 4 times higher among Negroes than among whites. As no quantitative information is available regarding other classes of detrimentals, the magnitude of the total genetic load in both groups is unknown. From the present data, it seems more reasonable to admit that the lethal equivalents operating both in whites and Negroes form mostly a mutational load and are also somewhat deleterious in heterozygotes. The present data apply exclusively to the Brazilian populations investigated and cannot be extrapolated to groups living in other areas, even if these groups present ethnic similarities to those which have been studied here. These conclusions must be accepted much more as working hypotheses than as definitive explanations of the findings.