Comparative Avian Cytogenetics: A Review

Avian cytogenetic research has, until recently, lagged far behind efforts devoted to the cytogenetics of other vertebrate groups. Avian chromosomes are inherently difficult to study because most are minute and their morphology and number are obscure. Since 1966, improved methods of culturing avian cells have resulted in more comparative chromosome studies whose quality parallels those for mammals. Recent activity in comparative avian cytogenetics now allows us to assess such factors as the overall karyotypic variability in birds and to consider the role that chromosomal change plays in avian speciation. In the present study, chromosomal variability was assessed within and among species of the same genus and within orders of birds. Chromosomal differences among local populations appear to be associated either with mechanisms that support balanced polymorphism or frequency dependent selection and not with speciation. The data are discussed in light of current models of chromosome evolution proposed for vertebrates other than birds.