A Study of Meiosis in Perennial Teosinte, in Tetraploid Maize and in their Tetraploid Hybrid

Abstract

Perennial teosinte was found to be a modified autotetraploid with a reduced chiasma frequency and an extension of chiasma interference across the centromere. This apparently simple modification has reduced quadrivalent frequency and has restricted quadrivalent types to rings and chains. Meiosis is nearly always regular and 93% of perennial teosinte seedlings were euploid. It is considered that since chromosome stability may be so easily attained, autotetraploids may be an important source of evolutionary variation. Most maize quadrivalents are complex types, where the terms alternate and adjacent segregation cannot be applied. It is argued that genetic disjunction from quadrivalents should be considered to be at random since no conclusive evidence to the contrary is available. In the hybrid between 4 n maize and perennial teosinte, random disjunction of chromosome 6 quadrivalents satisfactorily accounts for the observed frequency of y individuals in the backcross progeny.