Gene Similarity of the Triticinae and the Study of Segmental Interchanges

Abstract

FOUR different manifestations of the concept of genetic similarity have been demonstrated in the sub-tribe Triticinae. Two of these are at the chromosome level and two are at the gene level. Sears¹ demonstrated that each chromosome of hexaploid Triticum has two genetically related chromosomes which are undoubtedly of common origin. These related chromosomes or homoeologues can replace one another without causing serious genetic imbalance. This homoeology extends beyond Triticum to the genera Secale², Agropyron³ and Aegilops⁴. Cytological similarity of chromosomes was established by Riley and Chapman⁵ when they demonstrated that particular non-homologous chromosomes of Triticum and of Triticum and Aegilops have the potential to pair or synapse with one another. Similarity at the phenotypic level of gene expression was examined in detail by Sears⁶ in his study of Neatby's virescent gene. He showed that there exist three genes affecting chlorophyll production in a similar manner. The three genes are carried on the three chromosomes of homoeologous group 3. We have demonstrated similarity at the level of enzymatic gene-products⁷ and the existence of isoenzymatic proteins which are capable of hybridization. These proteins are produced by a particular rye chromosome, its wheat homoeologue of the A genome and apparently the homoeologues of the other two wheat genomes. Recent evidence, which will be published in detail later, supports the involvement of the homoeologues of the B and D genomes. These four patterns of similarity are compatible with one another.