Genetic Analysis of Wheat Chromosomes: I. Description of Proposed Methods

The F1obtained from crossing a substitution line with the recipient variety will be heterozygous only for genes on one pair of chromosomes. Crossing-over at meiosis, therefore, will result in recombinations only with respect to genes carried by this pair of chromosomes. The products of such recombinations will be obtained as univalent chromosomes of monosomics when such F1's are used to pollinate a line of the recipient variety deficient (nullisomic or monosomic) for the chromosome under study. When the monosomics so obtained are individually selfed, approximately 25 per cent of the offspring will be disomic, and homozygous for the genetic constitution of the backcross monosomics. The relative frequencies of progenies with different genetic constitutions will indicate directly the number and arrangement of genes differentiating the donor from the recipient variety chromosome.Genetic differences can be determined specifically for chromosome arms if, instead of whole-chromosome deficient lines of the recipient variety, those with telocentrics are used.The possible usefulness of the method for breeding, as well as studies of evolution, is briefly discussed.