The evaluation of three-point crosses at the tetrad and random spore level leads to the conclusion that both chiasma and chromatid interference are absent in the fission yeast Schizosaccharomyces pombe.

N an individual heterozygous for an interchange between two non-homoloI gous chromosomes, the observed amount of gene recombination in an interstitial region depends on the frequency of the respective centromere disjunction types and upon the chiasma (crossover) frequency expected for the two interstitial regions of the interchange complex. An interstitial region is considered to be the chromos...

Chiasma frequency was determined from total chiasma counts, and the distribution of these exchanges was determined by the ratio of proximal to distal chiasmata. No effect of trisomy IO could be demonstrated. Confirmation was obtained of earlier work showing more proximal and fewer distal chiasmata in K10 plants than in controls. However, diakinesis data failed to confirm the ability of KIO to i...

The onion species AUium amplectans includes both a triploid and a tetraploid variety. By light microscopy both varieties appear to have normal synapsis during pachytene of meiosis. However, the triploid does not form chiasmata and exhibits almost total asynapsis following pachytene. The tetraploid forms at least one chiasma per homologue and retains pairing through metaphase I. Electron-microsc...