Cytological observations on a duck hybrid: Anas clypeata × Anas penelope

Abstract

The chromosomes of the two parental forms and those of the hybrid do not show any detectable numerical or large structural differences. The pairing in the hybrid is frequently abnormal in that both free ends (highly charged with stainable substances) of many chromosomes show strong pairing, while midsegments repel each other. This partial failure of paring suggests that in the two parental forms gene mutations rather than chromosomal structural changes are responsible for incipient divergence.It is suggested that the stainable substance of the chromosomes acts as a carrier mechanism ensuring orderly pairing, segregation and numerical constancy of bivalents in the hybrid where the partner chromosomes have become partly non-homologous.The distinction between long and short chromosomes is typical for the avian karyotype, its evolutionary significance is discussed.