Frequencies of Twelve Ascus-Types and Arrangement of Three Genes from Tetrad Data |
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Authors: | Satoshi Harashima and Yasuji Oshima |
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Institution: | Department of Fermentation Technology, Osaka University, Yamadakami, Suita-shi, Osaka 565, Japan |
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Abstract: | Equations expressing the theoretical frequencies of twelve ascus-types in the tetrad analysis of a triply heterozygous diploid are described. Using these equations, a mapping procedure for a gene X, is proposed. The procedure requires that two genes, X and Y, of the same phenotype be heterozygous and that the map position of Y be known, and that another standard gene, Z, show an independent phenotype from X and Y. This procedure does not require the laborious allelism test of the segregants to determine the allelic 2:2 segregation in tetrads for the X and Y genes, which is indispensable for mapping by the conventional procedure. The exact placement of the X gene on a chromosome is possible by the chi2 minimization procedure in comparison with the expected frequencies of the six ascus-types or four spore-types deduced from the twelve expected ascus-types to give the optimal fit with the observed data. |
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