Comparative Mapping Using Chromosome Sorting and Painting

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Abstract
The capacity to make whole chromosome-specific, fluorescence-labeled DNA probes, by random-primed polymerase chain reaction (PCR 1 ) amplification of flow-sorted chromosomes or from chromosome-specific libraries, has led to a novel method of comparative genome mapping at the cytological level. This method has been developed using mammalian species. It has been found that when a chromosome-specific (paint) probe from 1 species is hybridized in situ to the chromosomes of another species, the paint probe detects large regions of homology containing genes conserved between the 2 species. Sometimes the probe hybridizes to only 1 chromosome, indicating that the whole chromosome is conserved. In other cases, several chromosomes or parts of chromosomes are painted, indicating that interchromosomal rearrangements have occurred during divergence of the 2 species. In general, more closely related species show fewer rearrangements than more distantly related species. Thus, only 1 interchromosomal rearrangement is found between the human and chimpanzee karyotypes, whereas at least 150 rearrangements are estimated between human and mouse ( Nadeau and Taylor 1984 ). An important exception to this rule is the extensive rearrangement found between human and the lesser apes, greater even than that observed between humans and Old World monkeys.