Exons can be independently gained or created in genes by exon shuffling, duplication and mutation of intronic sequences, especially repetitive elements as Alu. Such new exons are more prone to be alternatively spliced, included in transcripts in low frequencies and evolve faster than ancient exons. Alternative splicing is an important component of the evolution of new exons since it allows new gene parts to be slowly added to existing genes without compromising the original protein function. Eventually, new exons may be integrated to the original gene and evolve new functions. Keywords: exon birth; exon evolution; alternative splicing; exonization of Alu elements
