You are a conservation biologist, studying genetic variation in three populations of an endangered species of ladybug beetle. Population 1 has 20 beetles, two of which have brown spots, a recessive trait; the other nine beetles have red spots. Population 2 has 150 beetles and 15 of them have brown spots, while 135 have red spots. Population 3 has 50 beetles, and five of them have brown spots. In which population is the frequency of the allele for brown spots the highest?