U.S.-Argentina Cooperative Research on Systematics of the American Marsupials Using Single-copy DNA-DNA Hybridization

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This award supports the participation of Prof. John A. W. Kirsch of the University of Wisconsin-Madison in a program of cooperative research with Prof. Osvaldo Reig of the University of Buenos Aires aimed at using the latest techniques of biochemistry and genetic analysis to clarify the taxonomies of sister-group relationships among various marsupials. An additional object of this research is to test the proposition that the average rate of evolution in DNA is both regular and the same in mammals as in birds. Determining the taxonomies among the major groups of marsupials can be of great use, first in understanding processes of evolution and, eventually, in obtaining a complete description of the sequence of evolution in both marsupials and in man. It is believed that biochemical signatures--e.g., genomes--evolve as regular functions of time and therefore, each of different lines derived from a common ancestor evolves at the same rate. Given this evolution, the amount of divergence between any two lines will be proportional to the time elapsed since their most recent common ancestor, and the sequence of branching points among all lines may be accurately reconstructed. The researchers involved in this project will use single-copy DNA-DNA hybridization, a relatively simple technique of comparing the DNA from two species, in order to assess the magnitude of DNA complementarity. Genetic variability will be analyzed using electrophoretic techniques, and chromosomal development will be studied using direct chromosome-chromosome comparison techniques. The U.S. investigators are expert in hybridization studies, while their Argentinian collaborators will perform the remainder of the analytical studies; both groups will be involved in the collection of sample material in Argentina and the U.S. Verification that structural genes evolve in a predictable fashion with time would be important in demonstrating that the degree of chemical similarity among organisms is proportional to their "relatedness"--or degree of common ancestry--and a biochemically based time-developing sequence of evolutionary branching points from common ancestors should become possible based upon this theory.