An oocyte (egg-cell) contains a nucleus with a haploid chromosome number (n) and a cytoplasm with multiple template mitochondria. A sperm cell, also with a haploid nucleus (n), is motile, and its motility requires ATP from active mitochondria performing oxidative phosphorylation (OXPHOS). Following fertilization, active sperm mitochondria are degraded, leaving only the maternal, template mitochondria in the cytoplasm of the diploid (2n) zygote (or fertilized egg). Successive cell divisions in embryogenesis involve mitosis and differentiation, and division, of most template mitochondria into active, OXPHOS mitochondria, which eventually dominate and populate somatic tissues and the male germ line. However, some cells are sequestered and continue to carry only quiescent, template mitochondria, through meiosis and oogenesis to give the oocytes of females in the next generation. These cells comprise the female germ line. Female germ cells are never supplied with ATP by oxidative phosphorylation in their own mitochondria, but depend for their maintenance, at low metabolic rate, on ATP supplied, directly or indirectly, by neighbouring somatic cells (follicle cells). This hypothesis, after Allen (1996), predicts that the female germ line forms an indefinitely replicating vehicle for accurate transmission of mitochondrial DNA between generations.
Graphic by Wilson de Paula.
de Paula WBM, Agip A-NA, Missirlis F, Ashworth R, Vizcay-Barrena G, Lucas CH, Allen JF (2013) Female and male gamete mitochondria are distinct and complementary in transcription, structure, and genome function. Genome Biology and Evolution 5: 1969-1977. doi:10.1093/gbe/evt147.
Research | John F. Allen web page