This is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. It is often used to refer to the hooked structures found on arthropods.

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).