Reciprocal chromosome painting illuminates the history of genome evolutionof the domestic cat, dog and human

Domestic cats and dogs are important companion animals and model animals in biomedical research. The cat has a highly conserved karyotype, closely res embling the ancestral karyotype of mammals, while the dog has one of the mo st extensively rearranged mammalian karyotypes investigated so far. We have constructed the first detailed comparative chromosome map of the domestic dog and cat by reciprocal chromosome painting. Dog paints specific for the 38 autosomes and the X chromosomes delineated 68 conserved chromosomal segm ents in the cat, while reverse painting of cat probes onto red fox and dog chromosomes revealed 65 conserved segments. Most conserved segments on cat chromosomes also show a high degree of conservation in G-banding patterns c ompared with their canine counterparts. At least 47 chromosomal fissions (b reaks), 25 fusions and one inversion are needed to convert the cat karyotyp e to that of the dog, confirming that extensive chromosome rearrangements d ifferentiate the karyotypes of the cat and dog. Comparative analysis of the distribution patterns of conserved segments defined by dog paints on cat a nd human chromosomes has refined the human/cat comparative genome map and, most importantly, has revealed 15 cryptic inversions in seven large chromos omal regions of conserved synteny between humans and cats.