Final answer:
A change in the genetic material causing new variation is called a mutation, which is the primary source of new alleles and plays a key role in evolution by contributing to genetic diversity.
Step-by-step explanation:
A change in the genetic material that leads to new genetic variation is called a mutation. A mutation is a heritable change in the DNA sequence of an organism. The altered DNA can lead to changes in the structure and function of proteins, which can ultimately change an organism's phenotype — the observable characteristics. Genetic diversity in a population comes from mutation and sexual reproduction, with mutations being the primary source of new genetic material, or new alleles. Mutations can vary in effect, resulting in altered fitness or neutral outcomes where the phenotype is unaffected. Over time, this genetic diversity is the basis of natural selection, leading to evolution.