Proposed scenario for the evolution of KCNA genes and clusters in vertebrates. Names of genes are indicated inside or below boxes showing KCNA genes. In the human genome, there are eight KCNA genes, six of which form two tri-gene clusters (KCNA6-1-5 and KCNA3-2-10). The human KCNA clusters are positioned on chromosomes 1 (KCNA6-1-5) and 12 (3-2-10). Except for KCNA7, which has one intron, all vertebrate KCNA genes identified so far are intronless. The status with a single tri-gene cluster is hypothetical.