Allele:An allele is a variant form of a given gene, meaning it is one of two or more versions of a particular gene that exist within a population. In our ice cream analogy, alleles would be like different variations on chocolate - dark chocolate, milk chocolate, white chocolate.
Gene Pool:The gene pool is the set or 'pool' of all genes present in a population at any one time. This would be like all the possible ice cream flavors available in your city at any given time.
Biodiversity:Biodiversity refers to the variety and variability among living organisms from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes they are part; this includes diversity within species (genetic diversity), between species and ecosystem diversity. So biodiversity would include not just our ice cream shop but also bakeries, candy stores, smoothie shops - all places where you can find sweet treats!