Randomness of Mating in Isolated Polycross Plantings of Maize.

ATING of any naturally outbreeding organism is commonly assumed to be AI at random in the absence of artificial controls. This assumption is basic to many of the mathematical models used in population genetics. I t may have validity for animals, particularly in populations of relatively long standing. In some plants, however, differences in time of maturity of the male and female flowers arising from either morphological pattern or environmental conditions may limit randomness of mating. In corn, for example, a wide variation exists in time of flowering in any open pollinated variety. This variation results in a series of subpopulations, each with some degree of physiological isolation but with opportunity for gene transfer between subpopulations. Departures from random mating would be of particular importance in new populations that might result from the production of synthetics or the truncated sample from any of the various recurrent selection techniques. Since these methods of breeding are being used extensively, it appeared that information on randomness of mating was of sufficient importance to warrant investigation.