Genetic variation and origin of the most chromosomally polymorphic natural mammalian population.

Examination of allozymic variation in a chromosomally highly polymorphic population of Oryzomys documented that the sample consisted of two species, one that was chromosomally monomorphic and the other containing nine centric fusion polymorphisms. The existence of allozymic variation indicates that it is highly improbable that the polymorphic sample was the result of hybridization. These centric fusion polymorphisms appeared to cause little or no negative selection.