Nuclear DNA contents were estimated by microdensitometry in five species of Akodon rodents:Adodon molinae, A. dolores, A. mollis, A. azarae, Bolomys obscurus) and in three chromosomal varieties of A. molinae (2 n=42; 2 n=43, 2 n=22). The data obtained showed that the species with the highest DNA content was B. obscurus, followed in order of decreasing genome size by A. molinae, A. mollis, A. dolores and A. azarae. In A. molinae the forms with 2 n=42 chromosomes had the lowest and the forms with 2 n=44 the highest amount of DNA, while the forms with 2 n=43 had intermediate DNA contents. The variation in DNA amount detected in A. molinae was interpreted as a phenomenon of amplification occurring in the chromosomal areas involved in the chromosomal rearrangement giving rise to the polymorphism exhibited by this species. The DNA contents of shared chromosomes (chromosomes with similar size, morphology and G banding pattern, which are found in two or more phylogenetically related species), were compared and correlated with values of total nuclear DNA. The information obtained indicates that: (a) shared chromosomes have variable amounts of DNA: (b) in a given species there is a correlation between the amount of nuclear and chromosomal DNA in most shared chromosomes (and perhaps in most of the chromosmal complement), e.g., the higher the amount of nuclear DNA, the higher the content of DNA in shared chromosomes; (c) some chromosomes may undergo processes of amplification or deletion restricted to certain regions and usually related with mechanisms of chromosomal rearrangements. The data obtained seem to indicate that the genome size of a species depends on the interaction of two independent mechanisms: (1) a general process of DNA variation which acts coincidentally in the same direction (gain or loss) in the whole chromosome complement without disturbing the mechanism of chromosome condensation producing G bands and (2) restricted processes of DNA variations (amplifications or deletions) which act on single chromosomes and which are in most cases related with chromosmal rearrangements.
ASJC Scopus subject areas
- Molecular Biology
- Biochemistry, Genetics and Molecular Biology(all)
- Ecology, Evolution, Behavior and Systematics
- Agricultural and Biological Sciences (miscellaneous)
- Agricultural and Biological Sciences(all)