Most moths of a particular population died when the chestnut blight fungus that they were dependent on got wiped out. but some moths did survive.
which mechanism explains the reason for this?
gene flow
genetic drift
natural selection

The correct answer is -

Genetic drift.

Explanation:

Genetic drift can be described as an evolutionary process that occurs by chance event, by which frequency of gene variant (also known as allele) within a particular population changes drastically.

In other words, it is a random phenomenon, which can lead to significant change in the allele frequency of a population.

As per the given information in the question, most of the moth population (that were dependent on blight fungus) died when the chestnut blight fungus got wiped out completely. Only few moths survived.

This will result in the drastic change in the frequency of allele within the population of moths.

Thus, it represents the phenomenon of genetic drift.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.