Effect of selection and linkage on inbreeding.
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In this paper some methods for testing for the presence of selection at a single locus in a single population are discussed. It is assumed that at that locus only two alleles are present, and that the allele frequencies are observed for a number of generations. Tests are derived for detecting heterozygote advantage, genic selection and more general selection. Some simulation studies illustrate the power, or lack of power, of the tests, and show the connection between on the tests and the theory of Watterson (1979, Advances in Applied Probability 11, 14-30).
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A transformation is proposed of the variables used for constructing genetic selection indices, such that the reparameterized phenotypic covariance matrix is identity and the genetic covariance matrix is diagonal. These diagonal elements play the role of heritabilities of the transformed variables. The reparameterization enables sampling properties of the index weights to be easily computed and formulae are given for data from half-sib families. The index is likely to be least stable when the transformed variables of low heritability have high economic weights, and the weights will have highest sampling variance when these heritabilities are nearly equal. It is suggested that the sample roots of the determinantal equation be inspected when constructing an index in order to give some guide to its accuracy.
Testing for random mating at an HLA locus is a difficult problem because of the highly polymorphic nature of the HLA loci. We discuss some methodological issues and propose several tests. A simulation study is conducted to evaluate these tests. The single allele test and the shared allele test deal with small sample sizes by aggregating the data in different ways. The shared allele test is found to be a more powerful method of detecting non-random mating patterns involving a deficiency or an excess of similar genotypes than the single allele test. We show that random mating of couple at the genotype level implies the random mating of couple at the allele level. Several multi-allele approaches are proposed for large population-based data sets. Among them, the corrected allele-table test performs better than the generalized Wald test in terms of power and size. These methods are then applied to an HLA data set of Caucasian couples, and no solid evidence for non-random mating at the HLA A, B, and DR loci is found.
Cell substrains with increased and decreased spontaneous levels of micronuclei have been obtained by artificial selection. Clones of the substrains were investigated for mitotic division fidelity. About 200 mitoses were investigated in each clone. Frequencies of mitotic abnormalities such as ana- and telophases with bridge, chromosome and fragment delays at ana- and telophases, scattered chromosomes, chromosomes dislocated from spindle at metaphases and tripolar ana- and telophases were significantly higher in substrains with increased level of micronuclei. This finding indicates that reasons for arising of spontaneous micronuclei and alterations in mitotic division fidelity are the same or closely related. These reasons can be amplified as a result of the artificial selection.