The haploid human genome is about 3 × 109 base pairs in size. Every time this genome is replicated about 0.3 mutations, on average, will be passed on to one of the daughter cells. We are interested in knowing how many mutations are passed on to the fertilized egg (zygote) from its parents. In order to calculate this number we need to know how many DNA replications there are between the time that one parental zygote was formed and the time that the egg or sperm cell that unite to form the progeny zygote are produced.
In the case of females, this number is about 30, which means that each of a females eggs is the product of 30 cell divisions from the time the zygote was formed (Vogel and Rathenberg, 1975). Human females have about 500 eggs. In males, the number of cell divisions leading to mature sperm in a 30 year old male is about 400 (Vogel and Motulsky, 1997). This means that about 9 mutations (0.3 × 30) accumulate in the egg and about 120 mutations (0.3 × 400) accumulate in a sperm cell. Thus, each newly formed human zygote has approximately 129 new spontaneous mutations. This value is somewhat less than the number on most textbooks where it's common to see 300-350 mutations per genome. The updated value reflects a better estimate of the overall rate of mutation during DNA replication and a better estimate of the number of cell divisions during gametogenesis.
Remember that the next time you start arguing with creationists about evolution or the fetus worshippers about what is or is not human - "the human species" is an amorphous concept. We are all mutants - a hundred times over.
Except that I seem to have missed out on the nifty powers and cool leather outfits.
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