The way a story's narrator and characters are presented and developed is called

I think characterization

Explanation:

Usually the way a character is presented is by the use of characterization to give them certain traits and qualities

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).