Comparative Gene Mapping Mapping Homologous Genes in Different Species Why? Understanding of mammalian chromosome evolution. Extrapolation of information from one species to another.
Major premises All extant mammals have essentially the same complement of genes, inherited from a common ancestor Extant mammals have widely divergent karyotypes, suggesting that genomic rearrangements have accompanied their evolution
Challenges Establishing homology of genes Orthologous genes In different species Parologous genes Gene families within a species Mapping difficult in some species Not all mapped markers are useful
Maps exist for: 12 of 203 primate species 5 of 1687 rodent species 3 of 238 carnivore species 3 of 192 artiodactyl species 1 of 17 perissodactyl species 1 of 65 lagomorph species 2 of 253 marsupial species 1 or 3 monotreme species Nine mammalian orders have no maps
Mapping Markers Type 1.. Highly conserved, usually expressed genes, not highly polymorphic Type 2.. Highly polymorphic, usually not expressed genes, not necessarily conserved across species
Comparative mapping methods ZooFISH (interspecific chromosome painting) Somatic cell genetics Radiation hybrids Linkage Interspecific hybird backcrosses
Definition of terms in comparative mapping Homology segment: chromosome segment marked by at least one gene that has been mapped in two or more species. Human -----A-------------- Mouse -------------A------
Definition of terms in comparative mapping Conservation of synteny: two or more homologous genes on the same chromosome, not necessarily in same order. Human ------A-------B---------C--- Mouse ----A-------C------B--------
Definition of terms in comparative mapping Conservation of linkage: conservation of synteny but also of gene order. Human --------A------B-------C--- Mouse -----A-------B------------C--
Conclusions Mammalian genomes are generally conserved Conservation is not uniform across species Human, cat, cattle highly conserved Human, mouse, dog more rearranged Comparative maps useful in gene discovery