Two-locus problems in transmission genetics of mitochondria and chloroplasts.

A problem in transmission genetics was studied theoretically by regarding a cell as a population of organelle chromosomes. A hybrid cell of the two strains is assumed to consist initially of equal numbers of the two types of nucleoids, each containing an equal number of chromosomes. The two parent strains have different alleles at the two loci, and the two-locus dynamics of the hybrid cell line was analyzed. Within each nucleoid, stochastic matching and gene conversion are assumed to occur between the chromosomes, and at a certain rate fusion and division are assumed to take place between the nucleoids within the cell. Under this model, the changes of average genotype frequencies at the two loci within a nucleoid and within a cell were formulated, and the final frequencies of recombinant chromosomes were obtained. Random segregation of nucleoids at cell division was incorporated into the analyses; in addition, the increase of homozygosity in the cell was formulated. The results may be useful for interpreting the observed data on organelle genetics of some species of algae and yeast.