How does genetic drift affect the population over time?

Answer 1

The effect a mutation has on a population depends on two factors: First, every new mutation has to overcome the effects of chance on its survival. New mutations,when they exist in only one or two individuals, are often lost from the population due to genetic drift, or chance. For example, the mutation may never make it into a gamete (egg or sperm) and be lost. Or the gamete carrying the mutation may not be involved in a fertilization. Or the individual carrying the mutation may not find a mate, or may be killed when young. It is estimated that 1 out of three new mutations, regardless of the selective advantage, may be lost this way. Secondly, the selective value of the mutation (given it has survived being lost early due to drift) can determine its affect on the population. If it is deleterious, selection will act to reduce its frequency or even eventually remove it. If the mutation is neutral, its frequency will drift up and down due to chance, eventually either being lost or fixed (reaching a frequency of 100%). If it has a selective advantage over other alleles, it may eventually become fixed as well--how long depends on the size of the population and the strength of the advantage.