Genetic variation occurs through genetic recombination. 2 different methods of genetic recombination are illustrated. In the first method, Upper A Upper A, aa, Upper B Upper B, b b form Upper A Upper A, Upper B Upper B, a a, and b b. These then go on to form Upper A Upper B, Upper A Upper B, a b, a b. In the second method, Upper A Upper A, a a, Upper B Upper B, b b form Upper A Upper A, Upper B Upper B, a a, and b b. These then go to form Upper A b, Upper A b, a Upper B, a Upper B.

Which method of genetic recombination is illustrated in the diagram?
independent assortment
fertilization
crossing over
sexual reproduction