What are two main sources of genetic variation?

Mutations and gene recombination

Explanation:

Mutations are changes in DNA sequence that can create genetic variation within the population and thus are the ultimate source of new alleles . Mutations are important for evolution because of their ability to form a new genetic variant (allele) that can be spread to the offspring.  If a new variant of a trait formed by a mutation is advantageous and helps the organism to survive and reproduce,  it is going to be favourable by natural selection. That  variation will more likely be passed to the next generation and remain over time.

Genetic recombination is a process that occurs during meiosis between homologous chromosomes and it involves exchange of genetic material between them. As a result, offspring inherits reshuffled alleles different than their parents.

Another sources of genetic variation are random mating and random fertilization.