The Genetics of Maize

Abstract

In a general botanical symposium such as this, it would seem that the broader and more recent aspects of this genetical subject should be of greater interest than the detailed, technical developments. The layman often becomes weary of the expert who delights in telling him'more and more about less and less.' Moreover, the time limit definitely precludes any very detailed presentation. Accordingly, I shall attempt a general picture of what has happened during the past decade in the field of maize genetics. Maize has now been sufficiently analyzed genetically and cytologically to make it reasonably certain that its chromosomal mechanism of heredity is of the orthodox or Drosophila-like type. The ten pairs of corn chromosomes undergo typical parasynaptic conjugation and assort at random. There are no major deviations from what might be called normal, neoMendelian inheritance. With the possible exception of a few 8-rowed varieties like the Black Mexican and Golden Bantam sweet corn, as well as some flint varieties, which possess more than 20 (21 to 28) chromosomes, maize is relatively free from abnormal cytology. Both the independent and linked types of inheritance prevail; and crossing-over occurs in microand megasporogenesis with almost equal frequency, albeit with some small variability. On the whole the genetic mechanism has proven remarkably stable; and has enabled maize geneticists to exchange material with assurance that they may still remain on speaking terms with their colleagues. The general botanist is perhaps interested in knowing the types of hereditary characters and the parts of the plant they affect, which have been discovered up to date. For this purpose I have prepared a chart in which are outlined the known hereditary characters of maize, showing the number of genes concerned in their development (table 1). First, we may direct attention to the hereditary characters that involve the entire plant. The most striking of these is that called Teopod