 In the chicken (Gallus gallus), the 161-amino acid vasotocin-neurophysin VT preprohormone is encoded by the gene AVP, which is considered homologous to the mammalian genes encoding arginine vasopressin.Removal of the 19-amino acid N-terminal signal peptide generates the prohormone, which is hydrolysed to AVT (derived from amino acids 20-28) and neurophysin VT (derived from amino acids 32-161).The existence of two AVT preprohormones with different sequences in fishes (such as chum salmon, Oncorhynchus keta) is evidence for gene duplication.