Structural and Functional Bases for the Action of the A Alleles in Maize

Analyses of crossover derivatives from certain heterozygotes carrying the Ab "allele" indicate that the separable elements of Ab reside in adjacent members of a duplication. Thus the occurrence, in association with crossing over, of more than one type of derivative from each of two such heterozygotes is taken as evidence of variable local synaptic patterns reflecting homology between the Ab members. Likewise, the isolation of the alpha or proximal component from homozygous Ab individuals in association with crossing over is explained on the basis of exchanges within obliquely synapsed members. This interpretation requires that the Ab complex is an adjacent, serial duplication. There is evidence for structural and functional variability among Ab complexes of different geographic origin.