Origins of primate chromosomes – as delineated by Zoo-FISH and alignments of human and mouse draft genome sequences

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Abstract
This review examines recent advances in comparative eutherian cytogenetics, including Zoo-FISH data from 30 non-primate species. These data provide insights into the nature of karyotype evolution and enable the confident reconstruction of ancestral primate and boreo-eutherian karyotypes with diploid chromosome numbers of 48 and 46 chromosomes, respectively. Nine human autosomes (1, 5, 6, 9, 11, 13, 17, 18, and 20) represent the syntenies of ancestral boreo-eutherian chromosomes and have been conserved for about 95 million years. The average rate of chromosomal exchanges in eutherian evolution is estimated to about 1.9 rearrangements per 10 million years (involving 3.4 chromosome breaks). The integrated analysis of Zoo-FISH data and alignments of human and mouse draft genome sequences allow the identification of breakpoints involved in primate evolution. Thus, the boundaries of ancestral eutherian conserved segments can be delineated precisely. The mapping of rearrangements onto the phylogenetic tree visualizes landmark chromosome rearrangements, which might have been involved in cladogenesis in eutherian evolution.