Natural selection is most likely to happen to have different effects on organisms with which pairs of alleles
a) aa and aa
b) aa and aa
c) aa and aa
d) aa and aa

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme