Kernel-weight effects and transmission of a partial trisome involving the long arm of chromosome 5 in maize

Effects of trisomy for a portion of the long arm of chromosome 5 of maize (Zea mays L.) were explored by using the B 5La element derived from the B–A translocation TB-5La. In one family, the B 5La chromosome was transmitted through the egg to half of the offspring; in two other families, the rate of transmission was 44 and 46%, respectively. From the reciprocal cross, only 5.6% of the progeny carried B 5La . The presence of the allele Pr (purple aleurone) on the partial trisome made it possible to study the effect of trisomy for a portion of the long arm of chromosome 5 on kernel weight. The trisegmental kernels averaged 11% lighter than their disomic sibs on seven ears and were of the same weight on one ear. It appears that the particular alleles of genes on B 5La originally reduced kernel weight, but one variant, presumably acquired by crossing over, did not. Crossover products involving an exchange between the translocation breakpoint on B 5La and the pr locus occurred at a rate of 8.3%.