The chromosomes of cockerels (Gallus domesticus) during meiosis.

The chromosomes in spermatogenic cells of 10 cockerels were examined. Prior to removing the testes, the birds had been injected with either 2.5 mg vinblastine sulfate or 5 mg colchicine, or were untreated. A cell suspension was made from small pieces of testis and slides were prepared using an air-drying technique. Pretreatments of the birds increased the numbers of spermatogonial and secondary spermatocyte cells at metaphase and rendered them more amenable to analysis. The modal number of macrochromosomes or bivalents was observed in 90.2% of spermatogonia, 98% of primary spermatocytes at diakinesis, and 94.2% of secondary spermatocytes. Polyploid cells at all stages were thought to be largely artifacts of the procedure. Aneuploidy was rare, being found in only 1% of secondary spermatocytes. It is estimated that between 56 and 66 chiasmata occur in the 39 bivalents; of these, an average of 28 are seen in the six macrobivalents. Average numbers were 8.1, 5.9, 4.6, 3.6, 2.4, and 3.5 for macrobivalents 1 through 5 and the Z respectively. The numbers of chiasmata differed significantly among birds but were not differentially affected by pretreatment of the birds.