By comparison, the mutation frequency in the whole genome between generations for humans (parent to child) is about 70 new mutations per generation.[85][86] In the protein coding regions of the genome, there are only about 0.35 mutations between parent/child generations (less than one mutated protein per generation).[87] Whole genome sequencing in blood cells for a pair of identical twin 100-year-old centenarians only found 8 somatic differences, though somatic variation occurring in less than 20% of blood cells would be undetected.[88]