The researchers traced 25 families among four generations of the Darwin-Wedgwood dynasty, which included a number of consanguineous marriages. The families had 176 children, 21 of whom died before age 10.
They then entered the data into a computer program that documented gene flow across the generations and calculated the inbreeding coefficient for these families. The resulting number represents the probability that within one's genetic code, an individual receives two genes identical by descent as a result of the common ancestry of his or her parents.
Darwin's children had an inbreeding coefficient of 0.0630, meaning that there is a 6.3 percent chance that identical copies of a given gene will come from each parent. This figure is nearly identical to the already-known 6.25 percent chance that offspring of first-cousin marriages will experience the same genetic effect.
That means if both the mother and father have a deleterious allele an allele is an alternate expression of a gene there is a 6 percent chance that offspring will receive both of those deleterious alleles and the related damaging effects will occur. Statistically, this translates into a roughly 2 percent chance that the children of first cousins will develop a congenital defect, Berra noted roughly the same order of difference in risks between a 30-year-old woman and a 41-year-old woman giving birth.
Darwin was concerned that his own ill health had been inherited by his children, though that was unlikely because he probably suffered from a parasitic disease rather than a genetic defect, Berra noted.
Instead, Berra and his colleagues suggest that Darwin's offspring might have had a higher chance of succumbing to such illnesses as TB an
|Contact: Tim Berra|
Ohio State University