If egg and sperm form first cell of baby, then why does mtDNA comes from mother only?

Question

If egg and sperm form first cell of baby, then why does mtDNA comes from mother only?

In: Biology

Answer 1

I vaguely remember reading about this in one of Dawkin’s books. As he put it – the answer is in the exception. There is one species where mtDNA *initially* comes from both parents^1 – the two mtDNA strains fight it out until one strain has complete possession. This is of course a waste of resources, so most species choose the egg’s mtDNA by convention. It may not entirely be convention though – mtDNA would slow down sperm so there would be selection pressure *against* them carrying it.

^1 This also happens very rarely in species (such as humans) where it *isn’t* the rule.