____________Genetic Drift us the situation when events CAUSE changes in frequency of alleles in a population.Drastic chages in the environment and it's conditions can cause drastic changes in the alleles just sometimes.You can't predict the outcome since it's genetic Drift, it happens by chance, It does not actually target any particular allele.Unlike in natural selection, natural selection targets the allele which is less ADAPTABLE to the environmental conditions.Like, for Example, We have 50 DOGS, Out of which 10 dogs have the same particular gene while the REST 40 have same but another gene.The chances are that those 10 dogs will not survive, Just because of the small number, they will vanish even if there was nothing WRONG with the gene itself.But suppose, on the other hand you have 10,000 dogs, out of which 5000 have a particular gene, it's not possible that all those 5000 dogs will die just by chance, in large population, genes are lost if they are harmful in any way, but in small population, the chances are higher that they will die by pure chance._______________Hope it helps!