Natural selection on polymorphisms in northeastern Brazil.
Year: 1966
Type: article
Study design: Observational Study
Abstract: DuRiNc THE PAST DECADE, nearly all population geneticists have come to accept, rightly or wrongly, Ford's (1940) dictum that polymorphisms are maintained by selection rather than by mutation and genetic drift. At least seven methods have been used to study the selective forces involved: (1) Identification of the relevant environmental differences between populations with high and low gene frequencies; (2) detection of systematic departures of genotype frequencies from HardyWeinberg equilibrium; (3) association between genotype and a specific type of morbidity or response to a specific agent; (4) analysis of adaptive trends in genotype frequency with age or among successive generations; (5) detection of different genotype frequencies in the two sexes; (6) measurement of fertility and mortality differentials among genotypes; (7) analysis of departures from Mendelian segregation frequencies. Each of these methods is subject to its peculiar errors. Environmental differences between populations may be irrelevant to a gene frequency difference; genotype frequencies may depart from Hardy-Weinberg equilibrium because of inbreeding, assortative mating, classification errors, or sampling of relatives; apparent phenotypic associations, temporal trends, and reproductive differentials may be due to population stratification and biased sampling; and segregation disturbances may be caused by technical errors, extramarital parentage, and unrecognized alleles or other complexities in formal genetics. Nor is this the end of problems in studying selective forces, which may vary from place to place and from time to time, involving such slight and perhaps compensatory shifts in fertility and viability as to defy direct analysis, especially if genetic differences are obscured by dominance, failure to distinguish among multiple alleles, or rarity of the critical genotypes. Largely to explore the selective forces maintaining human polymorphisms, a study was made of 1,068 families from northeastern Brazil (Morton, 1964). This population was chosen because it is high in fertility, genetic variability, consanguinity, and infant mortality. Our sample was taken from migrant fami-
Source: Europe PMC (PubMed Central)
Authors: N E Morton, H Krieger, M P Mi
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1905042672