Mitochondrial Transmission Genetics: Replication, Recombination, and Segregation of Mitochondrial DNA and Its Inheritance in Crosses

Abstract

Mitochondrial genes differ at the molecular level from eukaryotic nuclear genes in a number of interesting aspects of structure and function, as the papers in this volume attest. Even more striking are the differences in patterns of inheritance. In particular:Nuclear genes show biparental inheritance; each zygote produced in a cross contains one copy of every nuclear gene from each parent and transmits both copies to all the cells in the adult individual or clone. In contrast, mitochondrial genes most often show uniparental inheritance. In some species, zygotes contain detectable numbers of mitochondrial genes from only one parent; when both parents contribute many mitochondrial genes, the genes from one parent often disappear.

In the nucleus, alleles of a gene segregate only during meiosis, with rare exceptions. Mitochondrial alleles segregate with high frequency at mitosis as well as meiosis, a phenomenon called vegetative segregation.

Some understanding of why mitochondrial genes fail to obey Mendel’s laws is needed to assist in designing and understanding the genetic experiments used to study gene structure and function. Moreover, mitochondrial genes are proving to be useful and interesting subjects for the study of molecular evolution. To interpret the evolutionary data, we need a theoretical framework of organelle population genetics and evolution, which will differ in important respects from the existing theory for nuclear genes. Developing this body of theory will require a detailed understanding of the rules and mechanisms of mitochondrial gene replication, recombination, and segregation.

Traditionally, uniparental inheritance of genes in mitochondria or...