In previous papers we found that the frequency of B chromosomes in native races of maize varies considerably in different populations. Moreover, we found genotypes that control high and low transmission rates (TR) of B chromosomes in the Pisingallo race. In the present work crosses were made to determine whether the genes controlling B-TR are located on the normal chromosome set (As) or on the B chromosomes (Bs). We made female f.0B ϫ male m.2B crosses between and within high (H) and low (L)

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... R groups. The Bs were transmitted on the male side in all cases. The mean B-TR from the progeny of f.0B (H) ϫ m.2B (H) and f.0B (H) ϫ m.2B (L) crosses was significantly higher than that from f.0B (L) ϫ m.2B (L) and f.0B (L) ϫ m.2B (H) crosses. The results show that the B-TR of the crosses corresponds to the H or L B-TR of the 0B female parents irrespective of the Bs of the male parent. This indicates that B-TR is genetically controlled by the 0B female parent and that these genes are located on the A chromosomes.