Genetic Investigations in a Northern Brazilian Island

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Abstract
A Brazilian island with a total population of 307 inhabitants (sex ratio 89.5) was found to have a breeding population of 104 and an effective number of 94. Its total migration rate is 0.25 and the migration rate of its breeding population is 0.33. The corresponding effective migration rates are 0.18 and 0.29, respectively. Short-range migrants are 0.17-0.26, long-range ones 0.07-0.14. The whole population presents a marital distance of 88 km and a migrational distance of 68 km. Among consanguineous parties, these distances are lower than 1 km. The observed (estimated from pedigrees) inbreeding coefficient equals 0.0015, a value 5-9 .times. lower than theoretically expected (from 0.0077 to 0.0133, say roughly 0.01). It is also lower than those of other (inland) populations with about the same migrational rate. The inbreeding coefficient of the offspring of the consanguineous couples is also very low (0.0071). The prevailing mating pattern on the island may possibly be responsible for such avoidance of inbreeding. The value 0.01 is an estimate of the coefficient of kinship of the population. Prenatal mortality equals 8%; infant mortality 10%; mortality from birth up to the age of 20 is 18%. The average number of live-born children per woman at least 40 yr old is 7.80. The frequency of twin births is 1.07%.