bivalent

Its chromosomes associated as univalents, bivalents, trivalents and quadrivalents (Table 2).

mairei) using different genotypes, and they reported a mean of 9.23 bivalents and a high frequency of trivalents (1.17) and quadrivalents (0.60).

The results showed regular 10 bivalents, one by one synapses and one to one disjunction in B.

During meiotic stages, 10 bivalents and a univalent x chromosome were observed.

In most organisms, homologous chromosomes interchange their genetic content, undergoing reciprocal recombination events (chiasmata), which, in combination with sister chromatid cohesion, are responsible for the correct bi-orientation of bivalents at metaphase I and the subsequent segregation of a complete set of chromosomes at anaphase I.

In diplotene--metaphase I plates (n = 19), we observed at least one bivalent with two chiasmata and maximally four bivalents with two chiasmata.

The accession of Aster squamatus presented regular meiosis with 10 bivalents (II) in all the studies populations, according to presented results (Table 1).

caninus (PI 235438 and PI 252044) averaged 1.6 univalents + 13.1 bivalents + 0.03 trivalents + 0.03 quadrivalents per cell (Dewey, 1970), confirming that both species share the same basic genomes (StStHH).

In female meiosis, recombination can potentially occur along the entire length of the XX bivalent. In male meiosis, however, all X-Y recombination is restricted to the pseudoautosomal region, and therefore the amount of X-Y crossing over per unit length is considerably higher than for a comparable chromosomal segment in XX bivalents.

Bivalents measurements were made using the computer application Micromeasure version 3.3 (Reeves & Tear 2000).