title: Frequencies of twelve ascus-types and arrangement of three genes from tetrad data.
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.
mesh_terms: D002874:Chromosome Mapping; D003434:Crossing Over, Genetic; D005787:Gene Frequency; D005796:Genes; D005816:Genetic Complementation Test; D008040:Genetic Linkage; D006579:Heterozygote; D008433:Mathematics; D008540:Meiosis; D008954:Models, Biological; D010641:Phenotype; D012441:Saccharomyces cerevisiae; D013172:Spores, Fungal