sperm

Tuesday, I referred to mtDNA and sperm evolution. The topic was covered in some detail in a 2004 review paper by Neil Gemmell and colleagues, entitled, "Mother's curse: the effect of mtDNA on individual fitness and population viability."

The basic idea:

1. Mitochondrial DNA is maternally inherited, so that the mtDNA germline leading to any male is female all the rest of the way back in time.

2. Hence, any male's mtDNA would have been subject to selection only for success in females, never males.

3. But male traits depend on the adequate function of mtDNA genes, possibly differently from females.

Sperm stand out as a male-only cell type that place special requirements on mitochondrial function. The midsection of each sperm cell is composed largely of mitochondria packed together to provide energy for the flagellum. In humans, several mitochondrial disorders are known to induce infertility by means of reducing sperm motility.