The program "Nb_HetEx" estimates the effective number of breeders (N(b)) that produced the sampled progeny based on genotype counts contained in that sample. When the number of breeders is very small, there is an excess of heterozygotes in their progeny: the smaller the number of breeders, the larger the heterozygote excess. The Nb_HetEx program also estimates N(e) through the temporal method.
The effective number of breeders (N b ) for a cohort of progeny can be estimated from an excess of heterozygotes that arises in progeny produced by finite numbers of parents. In principle, N b is a simple function of the standardized deviation (D) of the proportion of heterozygous progeny from its expectation under random mating. We explored the sampling properties of this Destimator of N b through computer simulation. The accuracy of the D-estimator is remarkably robust to variation in numbers of alleles and loci and the presence of rare alleles, though precision can be low if, relative to a given N b , the sample of progeny or the cumulative number of independent alleles (n ci ) sampled is too small. For N b up to 30 parents, acceptable accuracy is achieved with sample sizes of 200 or more progeny and 80 or more independent alleles; for N b of 50-100, a sample of 500-1,000 progeny and 450-900 independent alleles are required for similar accuracy and precision. Though the estimator is most applicable for the situation of random union of gametes (as may occur in some marine invertebrates or fish, for example), it works for other mating systems (monogamous or polygamous pairings, polygyny), when the effective number of breeders is small (N b B 20). Simulations reveal small overestimation biases with smaller sample sizes, rare alleles, or highly polymorphic loci (C10 alleles). Despite this bias, multiallelic loci are preferable to many loci with few alleles, which have larger sampling errors.
Variation of mitochondrial DNA (mtDNA) was examined in nine populations from three lake-river systems of Chukotka and Kamchatka. Significant differences were found between most of the sockeye salmon samples studied. The genetic differences among populations were not high and often did not correlate with the geographical distances between them. The low population divergence is explained by a short time of existence of most of them, having been formed after the recession of the upper Pleistocene glacier. When the populations were grouped according to their spawning biotopes (river or lake), they in general appeared more genetically similar than upon their grouping by geographical location (the lake-river systems). The differences between the river and lake populations in the lake-river systems increased from north to south.
GENERAL GENETICSRUSSIAN JOURNAL OF GENETICS Vol. 41 No. 5 2005 BRYKOV et al .
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