Heteromorphic bivalent association at meiosis in bread wheat

Abstract

Crosses were made between 51 different pairs of ditelocentric lines of hexaploid bread wheat (Triticum aestivum L.) to give double-monotelodisomic progeny with two different telocentric chromosomes. All the crosses involved pairs of chromosomes from the same genome.At meiosis, the two telocentric chromosomes paired with their normal homologous partners to form heteromorphic bivalents which could be distinguished from the other rod and ring bivalents at metaphase I-they were morphologically marked. The position which each marked bivalent occupied across the metaphase plate was scored in 5209 light-microscope equatorial squashes of pollen mother cells at metaphase I.There was a strong tendency for the marked bivalents to be positioned towards, or at, the outside edge of the plate. This occurred in all the hybrid lines, and showed that morphologically marked bivalents do not behave like their normal homologues, at least in this hexaploid species. However, the crosses involving marked chromosomes in the B genome tended to have the marked bivalents lying more often at the outside of the plate than did the crosses involving marked chromosomes from the A and D genome. Thus the genomes were behaving differently, and it is possible that the three genomes are spatially separated in the nucleus.

Centromere Size Scales With Genome Size Across Eukaryotes

“…They also surmised that the total centromere area is equally distributed to individual chromosomes [6]. Individual centromeres of uniform sizes could contribute to proper congression and segregation because chromosomes with too large or too small functional centromeres tend to missegregate and get lost [15][16][17][18][19]. This would also mean that, within a karyotype, functional centromere size does not vary with chromosome size, a notion that has been supported by showing that small chromosomes of maize introduced into oat equalized their centromere sizes with large chromosomes of oat [9].…”