small effect size. To detect such small genetic effects, there is a growing interest in high throughput genotyping technologies that examine large numbers (e.g., 500,000) of single nucleotide polymorphisms (SNPs) densely mapped across the entire genome. Using these more incisive genome-wide association (GWA) scans, recent studies have reliably identified common variants associated with complex traits and diseases that include BMI (8, 9), height (10, 11), inflammatory bowel disease (12, 13), and type 1 and type 2 diabetes (13, 14). So far, only one GWA study of a personality trait has been published (15). That study used DNA pools from about 2000 individuals with extreme scores, but the results were limited to Neuroticism, only one of the five broad dimensions of personality.
