Two insulin genes are present in the salmon genome.

According to the accepted hypothesis, polyploid evolution is necessary to achieve meaningful gene duplication. Some fish, namely those belonging to the suborder Salmonidae, appear to be autotetraploid species that probably originated from a diploid ancestor relatively recently and that appear to be progressing toward diploidization to various degrees. The Pacific chum salmon (Oncorhynchus keta) has almost completed this process of diploidization. Thus, with regard to practically any gene product, theory predicts a freshly diploidized, autotetraploid species to possess twice the number of gene loci as diploid animals. Here we show that the chum salmon genome contains two nonallelic insulin genes that are both expressed in chum salmon Brockman bodies. Nucleotide sequence analysis reveals structural diversification of this pair of duplicated genes.