One microgamete penetrates the macrogamete and the remaining three die off. During syngny, four microgametes associate with the macrogamete. Each gamete has only one nucleus and may be either a microgamete or a macrogamete. The microgametes are motile and must reach the macrogamete to fertilize it. The flagellated microgamete fertilizes the female macrogamete to produce a diploid cell called a zygote. The fertilized macrogamete now becomes an ookinete, which penetrates the body of the vector. Some trophozoites enlarge and become macrogamete, whereas others divide repeatedly to form microgametes (anisogamy).