GENETIC-ANALYSIS OF SYSTEMATIC MITOCHONDRIAL HETEROPLASMY IN RABBITS

One unusual property of rabbit mitochondrial DNA, (mtDNA) is the exist ence of repeated 153-bp motifs in the vicinity of the replication orig in of its H strand. Furthermore, every individual is heteroplasmic: it carries mtDNA molecules with a variable number of repeats. A systemat ic study of 8 females and their progeny has been devised to analyze mt DNA transmission through generations. The results suggest that three m echanisms are acting simultaneously. (1) Genetic drift in the germ lin e is revealed by the evolution of heteroplasmy when two major molecula r forms are present in a female. (2) A high mutation rate (around 10(- 2) per animal generation) generating molecular diversity, by deletion and addition of repeated units, is required to explain the observation of heteroplasmy in every individual. Moreover, the rates of mutation from the most frequent type to the other types are unequal. The deleti on of one unit is more frequent than a deletion of two units, which is in turn more frequent than a deletion of three. (3) Selection for sho rter molecules in somatic cells is probable. The frequency distributio n of mtDNA types depends on the organ analyzed (kidney-spleen and live r vs. gonads).