A TEST OF HOMOLOGY BETWEEN B CHROMOSOME OF MAIZE AND ABNORMAL CHROMOSOME 10 INVOLVING CONTROL OF NONDISJUNCTION IN BS

Nondisjunction of B and B-translocation chromosomes occurs regularly in maize at the second pollen mitosis (Roman, 1947; Blackwood, 1956). The mechanism of nondisjunction was studied using the A-B interchange, TB-9b. The B9 chromosome of the interchange undergoes nondisjunction at the second pollen mitosis, while the 9B chromosome does not (Roman, 1947). It was shown that the 9B chromosome must be present in a plant for nondisjunction of the B9 to occur. This is consistent with the reports of Roman on TB-4a (1949) and Longley on TB-10a (1956). It was also demonstrated that the influence of the 9B chromosome is limited to pollen grains containing it, and does not extend to all the pollen of a plant. A test of homology between the B chromosome and abnormal chromosome 10 was also made. The ability of abnormal 10 to substitute for the 9B chromosome and induce nondisjunction of the B9 was tested. Nondisjunction did not occur at a detectable rate in the presence of abnormal 10, and the results failed to support Ting's proposal (1958) concerning the origin of abnormal 10. © 1969 Springer-Verlag.