The ch468R allele was associated with higher dominance in a sample of chimpanzees living in Chimpanzee Sanctuary Uto. The association between this allele and dominance was not present among the wild-born sanctuary chimpanzees in Guinea or in the total sample. There was also a statistically non-significant trend suggesting that neuroticism in chimpanzees was associated with the ch468R allele in Chimpanzee Sanctuary Uto. Moreover, while this relationship was not statistically significant, the effect size and direction of the effect were comparable in the chimpanzee sample from Guinea. Finally, in the total sample, there was a significant association between the presence of the ch468R allele and higher levels of neuroticism. One possible reason for the failure to cross-validate the dominance findings is that the wild-born sanctuary chimpanzees were younger than those at Chimpanzee Sanctuary Uto. As such, the dominance dimension may not yet have as clearly been expressed as in the more mature individuals. A second possible explanation for our failure to cross-validate the dominance findings in the wild sample is because they were separated from their mothers early in life and may have been subjected to other trauma. There does appear to be evidence of an association between neuroticism and ch468R. This is consistent with earlier studies of humans and mice which found that Q468R mutations are associated with major depression and aggressive behavior, respectively. This is also consistent with a recent study which found that the 39-untranslated-region polymorphism of TPH2 in rhesus macaques was associated with aggressive behavior. The chimpanzee TPH2 polymorphism is a gain-of-function mutation, which increases serotonin biosynthesis. In other words, like the S allele of 5-HTTLPR which has been related to human neuroticism, the ch468R allele of the TPH2 gene works to increase serotonin storage in the synapse by Publications Using Abomle Ifenprodil increasing production of and decreasing the re-absorption of serotonin. One shortcoming of the present study was the small sample size and thus these results require replications in larger independent samples. A second shortcoming is our poor knowledge of the background of the chimpanzees which prevented us from testing for any gene by environment interaction effects. A third shortcoming is that, while we included a model for dominance effects, the mean neuroticism across genotypes were only suggestive with respect to whether the G allele was dominant, though this may reflect the small sample size of each group. Chimpanzees have highly-developed brains and exhibit a variety of psychological and behavioral traits in their elaborate social interactions. The present study is the first to identify a genotype related to a personality trait in chimpanzees. Understanding differences in the genes responsible for behavioral variation could lead to a better understanding of the evolutionary history of humans and chimpanzee, including hominization. The finding of similar associations between the TPH2 gene and phenotypes related to neuroticism in humans, mice and rhesus macaques suggests that the relationship between neuroticism and TPH2 has deep phylogenetic origins. This is the first report of a relationship between a personality trait and genotype in great apes. Genetic markers for behavior may be useful for primate conservation, welfare and management in zoos.