![]() reduced genetic variation from the original population.This small population size means that the colony may have: Founder effectsĪ founder effect occurs when a new colony is started by a few members of the original population. Their population has since rebounded to over 30,000 - but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. An example of a bottleneck Elephant seal image courtesy of David Smith, UCMP. Reduced genetic variation means that the population may not be able to adapt to new selection pressures, such as climatic change or a shift in available resources, because the genetic variation that selection would act on may have already drifted out of the population. This is illustrated by the bags of marbles shown below, where, in generation 2, an unusually small draw creates a bottleneck. Because genetic drift acts more quickly to reduce genetic variation in small populations, undergoing a bottleneck can reduce a population’s genetic variation by a lot, even if the bottleneck doesn’t last for very many generations. Population bottlenecks occur when a population’s size is reduced for at least one generation. Genetic drift can cause big losses of genetic variation for small populations. Information on controversies in the public arena relating to evolution.Alignment with the Next Generation Science Standards.The big issues – Pacing, diversity, complexity, and trends.Macroevolution – Evolution above the species level.Microevolution – Evolution within a population.Mechanisms: the processes of evolution – Selection, mutation, migration, and more.The history of life: looking at the patterns – Change over time and shared ancestors.An introduction to evolution: what is evolution and how does it work?.
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