The frequency of an allele in a fly population changes from 89% to 20% after three generations. which other events most likely occurred during the same time period?

The other events that most likely occurred during the same time period would be; An environmental change that did not favor the individuals in the population with the allele most likely led to the change in allele frequency; because the allele frequency decreased by so much, there would had to have been a decrease in the population within a three generation period of time.