Answer:
The population suffered a genetic bottleneck, which decreased genetic variation and thereby randomly increasing the frequency of harmful alleles
Explanation:
A population bottleneck, also known as genetic bottleneck, can be defined as a drastic reduction in the size of a population, which may be caused by anthropic activity and/or environmental phenomena (e.g., earthquakes, famines, fires, droughts, etc). A genetic bottleneck leads to a reduction in genetic variability within a population. Moreover, the genetic drifit caused by a genetic bottleneck can also increase the frequency of harmful alleles/mutations (it is due to the random sampling of individuals), thereby increasing the frequency of deleterious alleles/mutations in the population.