The presence of a genetic correlation between two tasks is typically taken to indicate the action of common genes in influencing performance in the tasks, a situation called pleiotropy. The implication is that a survey of genotypes in two similar tasks should result in a similar rank order of the genotypes; if the rank orders are different or the strain means do not correlate, the tasks could be measuring independent processes or genetically unrelated aspects of the same process (33). The reliability of each task must also be considered. A failure to find a large genetic correlation between two tasks does not necessarily mean there is there is no common genetic influence between the measures, but it could indicate that one or both of the tasks are simply not reliable enough to detect a correlation that might actually exist. Furthermore, detection of a genetic correlation depends on a measurable genetic contribution to each task, and the larger the genetic effect size for each trait, the more likely a genetic association is to be detected.
