Nullisomic Analysis in Common Wheat

Abstract

Four methods are outlined for using nullisomics and monosomics in wheat to locate genes on chromosomes: 1. Absence of effect of a particular gene in a particular nullisomic. This applies to ordinary dominants and certain recessives in any variety in which nullisomics are available. 2. Abnormal segregation in F2. A dominant gene in another variety gives an aberrant F2 ratio following crossing with a line nullisomic for the chromosome on which the gene is located. A hemizygous-ineffective recessive appears in normal frequency in F2, but is confined to disomic individuals. 3. Homozygosity of F2 disomics. Study of F3 populations shows in which F2 family all the disomic plants were homozygous for the gene in question. 4. Gene content of substituted lines. Each chromosome of the variety under test is transferred separately to a standard line, where its effects indicate what gene it carries. Certain recessive genes in wheat are ineffective in single dose (hemizygous), and their dominant alleles show no dosage effect. They are positively acting genes that require two doses to reach their threshold of expression.