Similarly to cats, chickens also lack functional Tas1r2 gene.[57,61] Interestingly, some other birds recognize sugar taste,[74,75] suggesting that they may have a functional T1R2. Thus, pseudogenization of Tas1r2 occurred multiple times in evolution. Loss of Tas1r2 in cats and chickens may be a consequence of their feeding behaviour that does not require a sweet taste receptor for proper food choice. However, a reverse causative relationship is also possible, when a loss-of-function mutation in the Tas1r2 gene resulted in loss of sweet taste sensation, which in turn altered feeding behaviour of these animals.
