It has been shown that thyroid hormones are important in development and growth in birds and further that thyrotropin (TSH) signaling regulated photoinduced seasonal reproduction. In addition to controlling the development of certain physiological traits, TSH can affect a wide range of phenotypes related to domestication such as behaviour, growth rate, more frequent reproductive cycle’s, pigmentation and also behaviour. Studies indicate that thyroid hormone physiology could potentially be responsible for differences in individual stress response as well as differences in social dominance. This project investigated behaviours expressed in the different genotypes on the Thyroid stimulating hormone receptor (TSHR) gene in chickens. Standard test such as Fear of human, Aerial predator, Tonic immobility and Social hierarchy were carried out with White leghorn (WL) as a domesticated species and Red Junglefowl (Rjf) as their wild counterpart; these were considered to be the control group. There was no significant result on genotype effect for the TSHR animals observed in those variables tested. The TSHR mutants were expected to mirror the White leghorn behavioural response and the TSHR wildtype the behaviour of Rjf. This was however not confirmed. There were a significant interaction between genotype effect and sex effect for TSHR for stand alert in the Aerial predator test which mirrored the results seen in the control groups. The male wildtype followed the male Rjf pattern however the mutant did not mirror the WL male. This study would benefit from more individuals to be tested, for stronger statistical results, plus also to have all genotypes represented to fully investigate the affect the TSHR mutation have on domesticated chickens and potentially the domestication process in a range of species. / TSHR