I remember a newspaper article on non-paternity that was an outgrowth of a study laying the groundwork for DNA testing. Two researchers in southern Florida looked at the birth records of children born at a local hospital or hospitals which included the child’s and their parents’ blood types. Just comparing the blood types, the researchers were able to identify cases of non-paternity: an A+ mom and a B+ dad can’t produce a O- baby. The researchers projected a non-paternity rate of 5%-8% with the suspicion that with the greater precision of DNA testing that it could climb to 10%.
Good timing. Cecil’s most recent column was on just this subject.
Long story short, several reports (pre- and post-DNA testing) made the papers claiming 10-30 percent non-paternity, but these were all pretty shaky. A couple of more rigorous studies (using DNA testing), on the other hand, estimate the actual rate among the general population is under 5%.
Actually, they could. The ‘O’ gene is recessive. The A+ mom could have a genotype of one gene for A, one for O. And one gene for + and one for -. The dad could have a similar genotype of BO and ±. Statistically, 1/4 of their kids will be AB, 1/4 AO, 1/4 AB and 1/4 OO. The latter will produce a pheonotype of type O blood. Similar pattern for Rh factor, except that since the Rh- gene is recessive, only 1/4 of their children will actually have the Rh- phenotype.