EVOLUTION OF MAMMALIAN GENOMES: CYTOGENTICS ASPECTS
Graphodatsky A.S.
Institute of Cytology and Genetics, SB RAS, Novosibirsk, RUSSIA
Comparative genome maps record the history of chromosome rearrangements that
have occurred during evolution.
The rates, types and directions of chromosomal
rearrangements as well as phylogenetic relationships can be inferred by comparative analysis
of the distribution patterns of conserved segments in different phylogenetic lineages. The
successful identification of chromosomal homology between species is fundamental for
comparative cytogenetic and genomic analysis. Cross-species chromosome painting, being
accurate, efficient, and suitable for genome-wide comparison, has become the method of
choice for comparative cytogentics, particaularly for comparing distantly-related species or
species with highly rearranged karyotypes.
The use of painting to identify regions of
chromosomal homology has allowed the transfer of information from map-rich species such
as human and mouse to a wide variety of other species. When combined with chromosome
banding and gene mapping, comparative chromosome painting can provide the most accurate
comparative chromosome maps for species being compared. From a painting analysis
spanning some mammalian taxa (Primates, Artiodactyla, Perissodactyla, Carnivora,
Lagomorpha, Rodentia and Afrotheria) three distinct classes of synteny conservation have
been designated: (1) conservation of whole chromosome synteny, (2) conservation of large
chromosomal blocks, and (3) conservation of neighboring segment combinations. This
analysis has also made it possible to identify a set of chromosome segments (based on human
chromosome equivalents) that probably made up the karyotype of the common ancestor of the
Placentalia orders. This approach provides a basis for developing a picture of the ancestral
mammalian karyotype and trends of karyotype and genome evolution in all these taxa.