Short answers, pulled from the story.
Genetic drift is the change in the frequency of an allele in a population due to random chance rather than survival advantage. Natural selection favors alleles that improve survival or reproduction and has a directional effect, while genetic drift is undirected and operates on neutral, beneficial, and harmful alleles alike.
Sewall Wright coined the term genetic drift. His first use of the word appeared in 1929, though at that time he was using it to describe a directed process. The random, sampling-error sense of the term was later formalized by Wright and became known as the Sewall-Wright effect.
A population bottleneck occurs when a population contracts sharply in size due to a random environmental event, leaving survivors chosen by chance rather than by any genetic advantage. The bottleneck amplifies genetic drift by drastically reducing the number of alleles carried forward, which can cause some alleles to be lost entirely and others to become fixed.
The founder effect is a special case of a population bottleneck in which a small group splits from a larger population and establishes a new colony. The Amish migration to Pennsylvania in 1744 is a well-documented example: two founding members carried the recessive allele for Ellis-Van Creveld syndrome, and because descendants remained relatively insular, the syndrome is now much more prevalent among the Amish than in the general population.
In 1968, Motoo Kimura argued in his neutral theory of molecular evolution that most genetic changes that spread through a population are driven by genetic drift acting on neutral mutations rather than by natural selection. This rekindled the long-running debate between those who, like Ronald Fisher, saw selection as the primary force in evolution and those who followed Sewall Wright's view that drift plays a significant role.
Greater prairie chicken numbers in Illinois fell from roughly 100 million birds in 1900 to about 50 birds in the 1990s due to hunting and habitat destruction. DNA analysis comparing mid-century birds to those from the 1990s documents a steep decline in genetic variation over just those few decades, and the species currently experiences low reproductive success.