Harashima S, Oshima Y
Genetics. 1977 Jul;86(3):535-52. doi: 10.1093/genetics/86.3.535.
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.
文中描述了在一个三重杂合二倍体的四分体分析中，表示十二种ascus类型理论频率的方程式。利用这些方程式，提出了一种针对基因X的定位程序。该程序要求同一表型的两个基因X和Y是杂合的，并且Y的图谱位置已知，以及另一个标准基因Z表现出与X和Y独立的表型。此程序不需要对分离体进行费力的等位性测试来确定四分体中X和Y基因的等位2:2分离，而这对于传统程序进行定位是必不可少的。通过chi2最小化程序，与从十二种预期ascus类型推导的六种ascus类型或四种孢子类型的预期频率相比，有可能将X基因精确地定位在染色体上，以使其与观察数据达到最佳拟合。
