The B chromosome of maize

Abstract

The B chromosome in maize is small and highly heterochromatic. Its presence or absence in a plant has no apparent effect on the organism and the B is considered genetically inert. Studies with the maize B chromosome can be divided into two general categories: (1) analysis of the chromosome itself, including its origin, evolution, gene constitution, and DNA content, and (2) utilization of the chromosome in translocations to manipulate segments of standard (A) chromosomes. In the first category, an important finding has been that several genes exist on the B chromosome which help maintain its presence in populations through a system of non‐Mendelian inheritance. In the second type of research, a number of methods have been developed for manipulating A chromosome dosage with B‐A translocations. Segmental monosomics, trisomics, and tetrasomics have been constructed. Applications of the techniques are found mainly in cytological localization of genes and in construction of gene dosage series.