Schild D, Mortimer R K
Genetics. 1985 Aug;110(4):569-89. doi: 10.1093/genetics/110.4.569.
Saccharomyces cerevisiae diploids homozygous for the rad52-1 mutation have previously been shown to lose chromosomes mitotically. Spontaneous events and events following low levels of X-ray or methyl methanesulfonate treatment result in monosomic diploids, whereas higher levels of treatment result in near haploidization. This rad52-1-dependent chromosome loss has been used to develop a new mapping method which can be used to assign a previously unmapped gene to a chromosome. Chromosome loss mapping can be done in either of two ways: if a diploid, homozygous for rad52-1 but heterozygous for a variety of other recessive markers, is constructed with an unmapped recessive mutation in coupling with known chromosomal markers, chromosome loss will result in the coordinate expression of the mutation and other recessive markers on the same chromosome; if, however, the diploid is constructed with the unmapped mutation in repulsion to chromosomal markers, then even haploidization will never result in the coordinate expression of the unmapped mutation and other markers on the same homologous chromosome pair--This mapping method and subsequent tetrad analyses have been used to locate hom6 on chromosome X, ade4 on chromosome XIII and cdc31 on chromosome XV and to demonstrate that met5, previously assigned to chromosome V, actually maps to chromosome X; the met- marker on chromosome V has been shown to be met6. GAL80 and SUP5, previously assigned to an unmapped fragment, have now been mapped to the right arm of chromosome XIII.
先前已表明，对于rad52 - 1突变纯合的酿酒酵母二倍体在有丝分裂时会丢失染色体。自发事件以及低水平X射线或甲磺酸甲酯处理后的事件会导致单体二倍体，而较高水平的处理会导致近乎单倍体化。这种依赖rad52 - 1的染色体丢失已被用于开发一种新的定位方法，该方法可用于将先前未定位的基因定位到一条染色体上。染色体丢失定位可以通过两种方式之一进行：如果构建一个对于rad52 - 1纯合但对于多种其他隐性标记杂合的二倍体，并使其与一个未定位的隐性突变与已知染色体标记处于顺式排列，染色体丢失将导致该突变与同一条染色体上的其他隐性标记的协同表达；然而，如果构建的二倍体中未定位的突变与染色体标记处于反式排列，那么即使单倍体化也永远不会导致未定位的突变与同一同源染色体对上的其他标记的协同表达——这种定位方法以及随后的四分体分析已被用于将hom6定位到X染色体上，将ade4定位到XIII染色体上，将cdc31定位到XV染色体上，并证明先前定位到V染色体上的met5实际上位于X染色体上；V染色体上的met - 标记已被证明是met6。先前定位到一个未定位片段上的GAL80和SUP5，现在已被定位到XIII染色体的右臂上。
