where the sum is over all loops by which the same gene might be passed down by different routes to the individual in question; fA is the probability of identity between the two genes of the ancestor in each loop.
HINT 15L: The formula in Box 15.3 gives the probability of identity by descent as
where the sum is over all loops by which the same gene might be passed down by different routes to the individual in question; fA is the probability of identity between the two genes of the ancestor in each loop.