'Alternate-2' disjunction does not exist

Abstract

John and Lewis (1965) proposed a model of disjunction of translocation of heterozygotes that defined two types of alternate disjunction, alternate-1 and alternate-2, differing from the classic view of only one type. Endrizzi (1974), and subsequent workers citing him, claim to have observed two distinct alternate disjunction configurations, corresponding to John and Lewis's alternate-1 and alternate-2 types, in meiotic preparations of several species. These observations are based on a two-dimensional interpretation of the three-dimensional phenomenon of disjunction, and are erroneous. In each case the two supposed types are topologically identical. There is only one possible alternate disjunction configuration.