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

The method of genetic recombination illustrated in the diagram is crossing over.