Construction and uses of new compound B-A-A maize chromosome translocations.

Maize B-A translocations result from reciprocal interchanges between a supernumerary B chromosome and an arm of an essential A chromosome. Because of the frequent nondisjunction of the B centromere at the second pollen mitosis, B-A translocations have been used to locate genes to chromosome arms and to study the dosage effects of specific A segments. Compound B-A translocations (B-A-A translocations) are created by bringing together a simple B-A translocation with an A-A translocation in which breakpoints in the A-A and B-A translocations are in the same arm. Recombination in the region of shared homology of these A chromosome segments creates a B-A-A translocation. Success in creating and testing for a new B-A-A translocation requires that the B-A translocation be proximal to the A-A translocation and that the A-A translocation be proximal to the tester locus. The breakpoints of most of the A-A translocations have been cytologically defined by earlier investigators. Previous investigators have produced 16 B-A-A translocations and one B-A-A-A translocation, which collectively define 35 A chromosome breakpoints. We have enlarged this group by creating 64 new B-A-A translocations. We present a summary of the total of 81 B-A-A translocations showing their distribution among the chromosome arms and the 163 cytologically defined chromosome segments delimited by them. We also illustrate the method of construction of these B-A-A stocks and their uses.