A sequence or chain of behaviour set off by a specific stimulus. The component responses are repeated almost identically with each presentation of the stimulus. Fixed-action patterns are based on a "genetic blueprint," and the environment simply initiates the sequence. For example, the male stickleback fish will aggressively defend its territory from male intruders during mating season. The fish shows a fixed sequence of threatening actions that are elicited by the red underbelly of an intruding male.