Pachytene Pairing in Autotetraploid Brassica

Pairing of chromosomes was studied at midpachytene from 237 associations of 4 homologous chromosomes in autotetraploid Brassica campestris var oleifera. The frequency and the mean number of exchange of partners fitted the Poisson distribution and there was no interference of one exchange on the chance formation of another in its neighbourhood. Exchange of partners was observed both in the heterochromatic and euchromatic regions of the chromosomes.

A positive correlation exists between the physical length of the chromosome and the mean number of exchange of partners. The mean number of pairing blocks was however found to increase with increase in the mean length of the chromosome upto a certain extent beyond which it decreased.