Genetic Drift

[vivatix]

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Can someone go over how to attack questions on this topic?

I thought genetic drift happens when there is a sudden change causing a random change in the allele makeup of the population. So I am confused about this question - choice B seems right - oil spills has a sudden effect and some seabirds will survive and others will die at random. Choice A - there is no selective pressure here, thermophiles are happy at the hot temperatures in the hydrothermal vents. Choice D - this will selectively kills off bacteria that don't have antibiotic resistance. Choice C - there is no pressure on the population - there is a bear population on an island and is isolated but there is no sudden threat.

 

[bee17]

Genetic drift is random in regards to an organism's genetic makeup. For choice B, you don't know that seabirds will die at random; maybe some seabirds have a mutation that allows them to survive at higher frequencies than other seabirds.

It's okay that there is no selective pressure on the population in C. Selective pressure would imply natural selection. You are looking for populations vulnerable to genetic drift. Choice C meets the criteria of a small, isolated population.

 

[vivatix]

So the criteria for genetic drift is

small, isolated population
random change
but it does not necessarily have to be sudden?

 

[bee17]

The population doesn't have to be small and isolated for genetic drift to happen, but it is more likely to happen in that type of population. Genetic drift is simply a change in allele frequency in a population caused by random survival or reproduction. It doesn't have to be sudden, either. Let's say there are 8 bears in this population: 4 male and 4 female. In a breeding season, all the females are impregnated. Two of the females have three cubs each, while the two other females have one cub each. This differential reproduction would most likely cause a change in allele frequency in the population. But as long as the number of offspring was random (not due to allelic differences in the parents), then this is an example of genetic drift.