Answer: Genetic diversity.
Step-by-step explanation:
Sexual reproduction is the process by which male and female gamete fuse to form a zygote. In case of human beings crossing over and recombination of chromosome takes place. This process allows the transfer of characters from both the parents.
This changes the physical appearance of the zygote which is not identical to the parents.
This physical change is observed due to genetic diversity that is found at genetic level.