In the wild, each species may exist as one population or multiple populations. Different populations correspond to defined areas – habitats.
The sum of all present alleles for a given gene in a given population is known as the gene pool.
This is essentially a way of thinking about all the individuals in a population contributing their alleles towards the overall allele frequency. The extent of different alleles present gives the genetic diversity of a population.
The allele frequency in a population’s gene pool can change as a result of selection. The effectors of selection can be varied, yet the outcome is similar: advantageous or preferred alleles and the traits associated with them increase in frequency, while detrimental or disfavoured alleles and the traits associated with them decrease in frequency.