The karyotype of Glycine soja and its relationship to that of the soybean, Glycine max.

Abstract

Glycine sofa, a wild species of Eastern Asia, is the closest relative of the soybean, Glycine max. Its chromosome number is the same as that of the soybean (2n=40). The chromosomes are small and difficult to manipulate. The quantitative methods used in studying G. max were employed to determine the genomic structure of G. sofa. The investigations included the matching of chromosomes to establish homoeologous pairs, the identification of those chromosomes which could be distinguished morphologically, and classifying numerically the chromosomes which could not be identified individually. An idiogram was prepared of the identifiable chromosomes and a standard karyotype of the whole genome is proposed. The karyotype consisted of 12 metacentric and 8 submetacentric chromosomes.The karyotypes of G. max and of G. sofa were then compared. The total length of the chromosome complement of G. sofa was found to be about 6-7 percent smaller than that of G. max. When the chromosomes of each species were matched with those of the other to determine homoeologous pairs, it was found that 16 of the 20 in the two genomes were morphologically similar.The four chromosomes which did not correspond morphologically were then examined in greater detail. On the basis of lengths and arm ratios, these differences were considered to have arisen from evolutionary changes in the chromosomes of a common ancestor to give rise to those of the present two species. Of the two more likely methods of change, it was considered that deletions in the karyotype of the ancestor to bring about the G. sofa chromosome configuration was more probable than duplication to develop the G. max karyotype. Details of the changes which may have occurred were given for each chromosome.