  Interlocus gene conversion (IGC) homogenizes paralogs. Little is known
regarding the mutation events that cause IGC and even less is known about the
IGC mutations that experience fixation. To disentangle the rates of fixed IGC
mutations from the tract lengths of these fixed mutations, we employ a
composite likelihood procedure. We characterize the procedure with simulations.
We apply the procedure to duplicated primate introns and to protein-coding
paralogs from both yeast and primates. Our estimates from protein-coding data
concerning the mean length of fixed IGC tracts were unexpectedly low and are
associated with high degrees of uncertainty. In contrast, our estimates from
the primate intron data had lengths in the general range expected from IGC
mutation studies. While it is challenging to separate the rate at which fixed
IGC mutations initiate from the average number of nucleotide positions that
these IGC events affect, all of our analyses indicate that IGC is responsible
for a substantial proportion of evolutionary change in duplicated regions. Our
results suggest that IGC should be considered whenever the evolution of
multigene families is examined.
