Cytogenetics of Hybrids between Zea Mays and Euchlaena Mexicana.

NDOUBTEDLY specific and generic as well as lesser differences may U be largely attributed to differences in the chromosomes. Detailed analysis of gene and chromosome differences between related genera is seldom possible because of sterility and lack of genetical or cytological information. A striking exception is provided by Zea mays L. and Euchlaena mexicana Schrad. Between these distinct species highly fertile hybrids are easily obtained. Genetic and cytological work with maize is sufficiently advanced to make analysis of hybrids profitable. Linkage groups as well as cytological markers have been established for all 10 chromosomes in Zea mays. In some cases the approximate position of genes on a chromosome has been determined. Some of the most useful chromosome markers have been obtained as a result of the recent work with segmental interchange strains. The meiotic prophase crosses and rings which appear in maize heterozygous for an interchange make identification of the chromosomes concerned relatively easy. A consideration of these facts led to the belief that hybrids of maize and annual teosinte would be exceptionally favorable material for cytogenetical studies. From the study of hybrids it was hoped that a clearer knowledge of the similarities and differences of the chromosomes of maize and its relative, annual teosinte, would be obtained. Knowledge of this kind is useful in estimating the evolutionary processes which have been effective in the differentiation of the two forms studied. Three varieties of annual teosinte are recognized : Florida, Durango, and Chalco. The latter two varieties have been found growing wild in Mexico (Collins, 1921), whereas the cultivated Florida variety is thought to have come originally from Guatemala. Recently, Collins (1932) has reported that an annual teosinte resembling the Florida variety has been discovered which is native to that region.