CHROMOSOME STUDIES IN BIRDS

The class Aves is a large & varied taxonomic group consisting of 8700 species, 70% of which have been worked out karyologically Avian chromosomes are characterised by a high diploid number. 61% of the species have a diploid number of 78-82. The chromosomes of the Birds are differentiated into macro and micro chromosomes: 70% of the species have 7-9 pairs of macrochromosomes, the rest are microchromosomes. Birds have been extremely conservative as for as chromosome number are concerned, both increases and decreases have been infrequent. Conservative trend is also apparent in the fact that banding pattern homologies exist in distantly related species. Robertsonian translocations have been a shaping factor in chromosomal evolution - as metacentric macrochromosomes increase when mircrochromosomes decrease; and conversely telocentric macrochromosomes are abundant in sps. with many (more than 60) microchromosomes.