1. Comparative Gene Mapping
Mapping Homologous Genes in Different Species
Why?
Understanding of mammalian chromosome evolution.
Extrapolation of information from one species to another.

2. 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

3. 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

4. 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

5. 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

6. Comparative mapping methods
ZooFISH (interspecific chromosome painting)
Somatic cell genetics
Radiation hybrids
Linkage
Interspecific hybird backcrosses

23. 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------

24. 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

25. 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--

26. 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