Chromosomes in birds (Aves): evolutionary implications of macro-and microchromosome numbers and lengths

The karyotypes of 234 bird species from published reports were analysed with respect to diploid number of chromosomes, number of macro- and microchromosomes, length of microchromosomes compared to macrochromosomes, and centromeric position. There seems to be a conservation of a standard bird karyotype with 16 macro- and 64 microchromosomes, giving the diploid chromosome number 80. However, in all orders investigated, there is a tendency towards reduction of the number of microchromosomes and increase in the number of macrochromosomes. We propose that the smallest macrochromosomes (nos. 7–10) have been created by Robertsonian translocations of larger microchromosomes and that translocation of microchromosomes to macrochromosomes shifts the centromeric position from telocentric to submetacentric or metacentric.