The allotetraploidization of maize : Part 3: Gene segregation in trisomic heterozygotes.

Allotetraploidization is the creation of artificial allotetraploids. Allotetraploidization of maize can be accomplished by concentrating differential pairing affinity (DPA) factors into lines by a recurrent selection breeding system. Selection will be based on changes in genetic ratios which are the result of changes in the relative frequencies of various pairing configurations caused by DPA. Part 1 of this series gave extensive data on gene segregation in trisomic and tetraploid heterozygotes. Some of these tetraploids behaved like segmental allotetraploids. Part 2 presented a model for gene segregation in segmental allotetraploids. This paper presents an analogous model for gene segregation in trisomic heterozygotes. The pairing configurations of trisomes are analyzed by considering pairing in single arms which then are combined to obtain pairing configurations for whole chromosomes. The chromosome disjunction patterns of the various pairing configurations are hypothesized and expected genetic ratios are given that result from different levels of DPA expressed in several hypothetical trisomes. The model analyzes the effect of random pairing in one arm and non-random pairing in the other arms. Also, the effect of crossing over is taken into account. Because crossing over rates are affected by the environment, part of the variability in the data (Part 1) is explained. In addition, an hypothesis is advanced to explain the frequent enhancement of pairing affinity following x-irradiation.