Molecular events during chromosomal divergence of the South American rodent Graomys griseoflavus

Graomys griseoflauvus (Waterhouse, 1837) is a South American phyllotine rod ent having an autosomal polymorphism produced by a sequence of Robertsonian fusions. The chromosomal divergence was correlated with the molecular orga nization of two satellite DNA families (EG250 and Hpa3.2) and the second in ternal transcribed spacer (ITSII) of ribosomal DNA. These studies were perf ormed by Southern hybridization on all G. griseoflavus karyomorphs and othe r closely related cricetids. When Graomys karyomorphs were compared, interk aryomorphic differences were found at the methylation pattern level of EG25 0 satellite and the molecular organization of Hpa3.2 satellite and ITSII. T he findings support the hypothesis that Graomys griseoflavus karyomorphs ar e evolving separately, probably driving a chromosomal speciation process be tween 2n = 42-41 and 2n = 38-34 individuals.