Answer; Genetic drift The mechanism of evolution that would have caused this change is genetic drift.
Explanation; Genetic drift refers to changes in allele frequencies due to random chance. Genetic drift will eventually lead to allele loss or fixation even in large populations, but will take many more generations to occur in large populations than small. It may rapidly alter allele frequencies when population size decreases; bottle neck effect and founder effect.
The answer is b. because you wouldn't want a daughter cell that didn't have <em>all </em>necessary to be a complete cell, and this could be messed up if the DNA didn't replicate prior to cell division
