For red flour beetles, the observed change in allele T can be compared with a migration model. The resident population had N=434 and allele frequency 0.24; 45 migrants or gametes arrived via occasional migrants between grain bins; the source frequency was 0.80. The observed frequency after 4 generations was 0.29, close to the weighted average expected after migration, and relative fitness was about 1.00 for carriers and noncarriers. Which explanation is most consistent with the population size, migration, and fitness data?