Mathematical studies are conducted on three problems that arise in molecular population genetics.... more Mathematical studies are conducted on three problems that arise in molecular population genetics. (1) The time required for a particular allele to become extinct in a population under the effects of mutation, selection, and random genetic drift is studied. In the absence of selection, the mean extinction time of an allele with an initial frequency close to 1 is of the order of the reciprocal of the mutation rate when 4Nv << 1, where N is the effective population size and v is the mutation rate per generation. Advantageous mutations reduce the extinction time considerably, whereas deleterious mutations increase it tremendously even if the effect on fitness is very slight. (2) Mathematical formulae are derived for the distribution and the moments of extinction time of a particular allele from one or both of two related populations or species under the assumption of no selection. When 4Nv << 1, the mean extinction time is about half that for a single population, if the two ...
We have identified the Hsp70 gene superfamily of the nematode Caenorhabditis briggsae and investi... more We have identified the Hsp70 gene superfamily of the nematode Caenorhabditis briggsae and investigated the evolution of these genes in comparison with Hsp70 genes from C. elegans, Drosophila, and yeast. The Hsp70 genes are classified into three monophyletic groups according to their subcellular localization, namely, cytoplasm (CYT), endoplasmic reticulum (ER), and mitochondria (MT). The Hsp110 genes can be classified into the polyphyletic CYT group and the monophyletic ER group. The different Hsp70 and Hsp110 groups appeared to evolve following the model of divergent evolution. This model can also explain the evolution of the ER and MT genes. On the other hand, the CYT genes are divided into heat-inducible and constitutively expressed genes. The constitutively expressed genes have evolved more or less following the birth-and-death process, and the rates of gene birth and gene death are different between the two nematode species. By contrast, some heat-inducible genes show an intraspecies phylogenetic clustering. This suggests that they are subject to sequence homogenization resulting from gene conversion-like events. In addition, the heatinducible genes show high levels of sequence conservation in both intra-species and inter-species comparisons, and in most cases, amino acid sequence similarity is higher than nucleotide sequence similarity. This indicates that purifying selection also plays an important role in maintaining high sequence similarity among paralogous Hsp70 genes. Therefore, we suggest that the CYT heat-inducible genes have been subjected to a combination of purifying selection, birth-anddeath process, and gene conversion-like events.
Abstract Approximate formulas for the mean and variance of the F ST or G ST statistic in a finite... more Abstract Approximate formulas for the mean and variance of the F ST or G ST statistic in a finite number of isolated populations are developed under the effect of random genetic drift. Computer simulation has shown that the approximate formulas give a fairly accurate result ...
ENETIC linkage or linkage of genes is one of the common genetic features G of all organisms from ... more ENETIC linkage or linkage of genes is one of the common genetic features G of all organisms from viruses to man. It may be of great concern to evolutionary geneticists how genetic linkage was developed and how the intensity of linkage has been adjusted in the evolutionary process. FISHER (1930) suggested that "the presence of pail-s of factors in the same chromosome, the selective advantage of each of which reverses that of the other, will always tend to diminish recombination, and therefore, to increase the intensity of linkage in the chromosomes of that species." He also recognized another agency which would increase recombination, namely, ithe constant spread of advantageous mutations which, unless they occur so seldom that each has become predominant before the next appears, can only come together in the same gamete by means of recombination. This problem was recently discussed at length but still semi-quantitatively by BODMER and PARSONS There is a large amount of evidence that linkage intensity is under genetic control (cf. . In Drosophila ananassue, for example, MORIWAKI (1940) identified a dominant gene, En-2, located on the right arm of the second chromosome, which enhances recombination between almost every pair of loci on the same chromosome in both males and females, while KIKKAWA (1937) found another gene (or genes) which induces crossing over in males in the third chromosome. and also reported several recombination-deficient mutants in Escherichia coli K-12, which are probably due to single-gene mutation. Further, the effectiveness of artificial selection in reducing or increasing recombination values was reported by DETELFSEN and ROBERTS (1921), PARSONS in Drosophila.
Mathematical studies are conducted on three problems that arise in molecular population genetics.... more Mathematical studies are conducted on three problems that arise in molecular population genetics. (1) The time required for a particular allele to become extinct in a population under the effects of mutation, selection, and random genetic drift is studied. In the absence of selection, the mean extinction time of an allele with an initial frequency close to 1 is of the order of the reciprocal of the mutation rate when 4Nv << 1, where N is the effective population size and v is the mutation rate per generation. Advantageous mutations reduce the extinction time considerably, whereas deleterious mutations increase it tremendously even if the effect on fitness is very slight. (2) Mathematical formulae are derived for the distribution and the moments of extinction time of a particular allele from one or both of two related populations or species under the assumption of no selection. When 4Nv << 1, the mean extinction time is about half that for a single population, if the two ...
We have identified the Hsp70 gene superfamily of the nematode Caenorhabditis briggsae and investi... more We have identified the Hsp70 gene superfamily of the nematode Caenorhabditis briggsae and investigated the evolution of these genes in comparison with Hsp70 genes from C. elegans, Drosophila, and yeast. The Hsp70 genes are classified into three monophyletic groups according to their subcellular localization, namely, cytoplasm (CYT), endoplasmic reticulum (ER), and mitochondria (MT). The Hsp110 genes can be classified into the polyphyletic CYT group and the monophyletic ER group. The different Hsp70 and Hsp110 groups appeared to evolve following the model of divergent evolution. This model can also explain the evolution of the ER and MT genes. On the other hand, the CYT genes are divided into heat-inducible and constitutively expressed genes. The constitutively expressed genes have evolved more or less following the birth-and-death process, and the rates of gene birth and gene death are different between the two nematode species. By contrast, some heat-inducible genes show an intraspecies phylogenetic clustering. This suggests that they are subject to sequence homogenization resulting from gene conversion-like events. In addition, the heatinducible genes show high levels of sequence conservation in both intra-species and inter-species comparisons, and in most cases, amino acid sequence similarity is higher than nucleotide sequence similarity. This indicates that purifying selection also plays an important role in maintaining high sequence similarity among paralogous Hsp70 genes. Therefore, we suggest that the CYT heat-inducible genes have been subjected to a combination of purifying selection, birth-anddeath process, and gene conversion-like events.
Abstract Approximate formulas for the mean and variance of the F ST or G ST statistic in a finite... more Abstract Approximate formulas for the mean and variance of the F ST or G ST statistic in a finite number of isolated populations are developed under the effect of random genetic drift. Computer simulation has shown that the approximate formulas give a fairly accurate result ...
ENETIC linkage or linkage of genes is one of the common genetic features G of all organisms from ... more ENETIC linkage or linkage of genes is one of the common genetic features G of all organisms from viruses to man. It may be of great concern to evolutionary geneticists how genetic linkage was developed and how the intensity of linkage has been adjusted in the evolutionary process. FISHER (1930) suggested that "the presence of pail-s of factors in the same chromosome, the selective advantage of each of which reverses that of the other, will always tend to diminish recombination, and therefore, to increase the intensity of linkage in the chromosomes of that species." He also recognized another agency which would increase recombination, namely, ithe constant spread of advantageous mutations which, unless they occur so seldom that each has become predominant before the next appears, can only come together in the same gamete by means of recombination. This problem was recently discussed at length but still semi-quantitatively by BODMER and PARSONS There is a large amount of evidence that linkage intensity is under genetic control (cf. . In Drosophila ananassue, for example, MORIWAKI (1940) identified a dominant gene, En-2, located on the right arm of the second chromosome, which enhances recombination between almost every pair of loci on the same chromosome in both males and females, while KIKKAWA (1937) found another gene (or genes) which induces crossing over in males in the third chromosome. and also reported several recombination-deficient mutants in Escherichia coli K-12, which are probably due to single-gene mutation. Further, the effectiveness of artificial selection in reducing or increasing recombination values was reported by DETELFSEN and ROBERTS (1921), PARSONS in Drosophila.
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Papers by Masatoshi Nei