What are three processes that contribute to genetic variation during sexual reproduction

Crossing over - often, the sister homologous chromosomes of a cell exchange genetic material through recombination of genes. Independent assortment/random fertilization - there are numerous variety of ways that the chromosomes of the gametes can combine, after meiosis, through fertilization to form a zygote Mutation - on rare occasion, there is a slight and random change in the genes of a gametic cell caused by environmental factors.