A generic life cycle of Plasmodium species. Sporozoites delivered from the salivary glands of a biting mosquito (8) enter the human bloodstream and are carried to the liver, where they infect hepatocytes (1) and produce liver-stage schizonts. These burst open to release merozoites, which enter red blood cells and undergo multiple rounds of replication as the erythrocytic schizont (3). The stages shown at (3) are those analyzed by Foth et al. . A minority of merozoites at each cycle form the sexual stage gametocytes (4), which persist in the blood until ingested by another mosquito. Within minutes, gametes differentiate in the mosquito gut and fertilization follows (5). The zygote then develops into an ookinete (6), which penetrates the gut wall to form another 'schizogonic' stage, the oocyst (7). Daughter sporozoites are released from the oocysts and invade the salivary glands (8). Gametocytes (4) are terminally arrested cells while within the bloodstream. The expression of many proteins required for gamete function just minutes after the parasite is ingested by the mosquito is under translational control. Sporozoites (8), which are similarly responsible for transmission between hosts, have not yet exhibited similar regulation of gene expression: note that their development in the new host is less urgent. Figure modified with permission from .