Chromosome banding studies of the Equidae

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Abstract
The chromosome banding patterns of all seven extant species of the horse family, Equidae, are presented. This mammalian family is composed of a single genus, Equus, notable for its rapid karyotypic evolution. Comparison of G-banded karyo-types has allowed the identification of similar elements in the various species. Chromosome fusions and inversions have been identified, but many rearrangements remain unidentified. In addition to conservation in G-banding patterns of the equine X chromosomes, another chromosome with a conserved G-banding pattern has been identified. Additionally, several examples of chromosomes with a unique G-banding pattern present in two or more species are described. The G-banding pattern of the chromosomes of E. zebra hartmannae (2n = 32) is unique and shows little resemblance to that of other Equidae. The pattern of constitutive heterochromatin, as determined by C-banding, shows alteration with the reduction in diploid chromosome number within the Equidae. Species with the highest diploid chromosome numbers display mainly centromeric C-bands, whereas species with lower diploid chromosome numbers display fewer C-banded chromosomes, and frequently when C-bands are present, they are not centromeric in location. The first description and cytogenetic study of a hybrid from the cross E. grevyi X E. burchelli antiquorum is presented showing extensive homologies between the G-banded chromosomes of these two species.