CYTOGENETIC STUDIES OF PRECOCIOUS MEIOTIC CENTROMERE DIVISION IN LYCOPERSICON ESCULENTUM MILL

Abstract

N the normal course of meiosis chromosome division is completed at the beginIning of AI1 and the sister chromatids migrate to opposite poles. When division occurs earlier, it is regularly associated with the presence of unpaired chromosomes in late PI or at MI and is very likely stimulated by this lack of pairing. Rarely precocious division may take place in the absence of reduced pairing. Unpaired meiotic chromosomes are present in organisms deviating from the diploid chromosome complement, in species hybrids with reduced chromosome homology, and in asynaptics. At AI in monosomics the univalent divides in almost all cells (OLMO 1936; SEARS 1952) or in about half of them (MORRISON 1953). The univalents of haploids usually segregate randomly to the poles during AI dividingrarely at this stage (BELLING 1927; IVANOV 1938; LEVAN 1942,1945). In a few haploids the unpaired chromosomes divide frequently in AI (GAINES and AASE 1926; LESLEY and FROST 1928). The reduction of pairing in trisomics, polyploids, and species hybrids can lead to univalents at MI, but their behavior as to time of division is often quite irregular even in the same material (LESLEY 1928; MCCLINTOCK 1929; UPCOTT 1935).