MOLECULAR KEYS TO SPECIATION - DNA POLYMORPHISM AND THE CONTROL OF GENETIC EXCHANGE IN ENTEROBACTERIA

Speciation involves the establishment of genetic barriers between clos ely related organisms. The extent of genetic recombination is a key de terminant and a measure of genetic isolation. The results reported her e reveal that genetic barriers can be established, eliminated, or modi fied by manipulating two systems which control genetic recombination, SOS and mismatch repair. The extent of genetic isolation between enter obacteria is a simple mathematical function of DNA sequence divergence . The function does not depend on hybrid DNA stability, but rather on the number of blocks of sequences identical in the two mating partners and sufficiently large to allow the initiation of recombination. Furt her, there is no obvious discontinuity in the function that could be u sed to define a level of divergence for distinguishing species.