Gene duplication is one of the main mechanisms of formation of new genetic material in evolution. The occurrence of a gene duplication is believed to relax selection pressure on one of the copies. Consequently, this gene accumulates mutations at a higher rate, and over time it acquires a new function. As a result of several rounds of polyploidization, many genes in salmon are duplicated, including the growth hormone gene. The analysis of nucleotide diversity in the paralogous genes of growth hormone, gh1 and gh2, demonstrated that the level of variability in their introns was higher than in the exons. In addition, the variability of each exon weakly correlated with its length, and seems to be determined by the functional significance of the protein region encoded. The level of variability in the exons of the gh2 gene was higher than that in the gh1 one, which was probably due to the current process of gene subfunctionalization.