Characterization of chromosome structures of Falconinae (Falconidae, Falconiformes, Aves) by chromosome painting and delineation of chromosome rearrangements during their differentiation

Karyotypes of most bird species are characterized by around 2n = 80 chromosomes, comprising 7-10 pairs of large- and medium-sized macrochromosomes including sex chromosomes and numerous morphologically indistinguishable microchromosomes. The Falconinae of the Falconiformes has a different karyotype from the typical avian karyotype in low chromosome numbers, little size difference between macrochromosomes and a smaller number of microchromosomes. To characterize chromosome structures of Falconinae and to delineate the chromosome rearrangements that occurred in this subfamily, we conducted comparative chromosome painting with chicken chromosomes 1-9 and Z probes and microchromosome-specific probes, and chromosome mapping of the 18S-28S rRNA genes and telomeric (TTAGGG) (n) sequences for common kestrel (Falco tinnunculus) (2n = 52), peregrine falcon (Falco peregrinus) (2n = 50) and merlin (Falco columbarius) (2n = 40). F. tinnunculus had the highest number of chromosomes and was considered to retain the ancestral karyotype of Falconinae; one and six centric fusions might have occurred in macrochromosomes of F. peregrinus and F. columbarius, respectively. Tandem fusions of microchromosomes to macrochromosomes and between microchromosomes were also frequently observed, and chromosomal locations of the rRNA genes ranged from two to seven pairs of chromosomes. These karyotypic features of Falconinae were relatively different from those of Accipitridae, indicating that the drastic chromosome rearrangements occurred independently in the lineages of Accipitridae and Falconinae.