Why are the bottleneck effect and founder effects considered genetic drift?
1 Answer
Genetic drift is the change over time of the relative frequencies of the alleles in a population (due to chance). It occurs especially in smaller populations.
The bottleneck effect is a situation that occurs when the number of individuals in a population is dramatically reduced (the founder effect also may fall into that, since only a small number of individuals are there to "found" a new colony/population.) In both cases, the population sizes are very small.
In both these cases, the individuals "left" due to this reduction is random; so no specific allele or characteristic is favored.
Because of this, there may be significant variations of the allele frequencies in the new population. This will, over time, change these frequencies in this population (compared to that of the original one): since these variations may cause one allele to have an exceptionally high frequency, the allele frequencies in the population may shift towards that one allele.
Likewise, if there are exceptionally low frequencies of one allele, the allele frequencies may shift against that one allele, or it may disappear from that population altogether.
Hope this helps!
