A Secondary Trisome in Maize

Abstract

This is the first secondary trisomic reported in maize and arose as a variant in the progeny of a selfed plant trisomic for chromosome 6. This secondary differed markedly from its sibs and when studied cytologically proved to be a secondary trisomic of chromosome 5. Characteristics which distinguish the primary trisomic of 5 were exaggerated in this plant. Cytological evidence shows that the two arms of the modified chromosome in this trisomic were of equal length; also, that this chromosome is composed of two entire short arms of 5 with a median insertion point. The two commonest types of configuration at diakinesis were a ring of three and a bivalent plus a closed uni-valent. The most striking feature of the diakinesis was the failure to find figure eights.