In Plasmodium , which causes malaria, fertilization of gametocytes...

In the life cycle of Plasmodium, gametocytes are formed in the red blood cells of the human host.

When a female Anopheles mosquito takes a blood meal from an infected person, these gametocytes enter the mosquito's gut.

Inside the gut (stomach) of the mosquito, the gametocytes mature into male and female gametes. Fertilization occurs here, leading to the formation of a diploid zygote.

The zygote then develops into a motile ookinete, which penetrates the gut wall to form an oocyst.

Answer: gut of a female Anopheles mosquito