Eukaryotic genes contain exons and introns. Exons contain information for polypeptide chain synthesis, so they are retained in the mRNA and are not ejected from the primary transcript. Introns do not contain information for polypeptide synthesis, so they are ejected from the primary transcript by the spliceing process. Eukaryotes contain all types of introns, and the most common are spliceosomal introns, which are associated with phenomena that have influenced the evolution of proteins. Exon shuffling allows the creation of proteins with new or altered functions faster than obtaining new proteins by mutations of existing ones. It is enabled by the repair of double-stranded breaks by non-homologous recombination and the correlation of exons with the structural domains of proteins. Thus, most eukaryotic proteins with repeating domains were obtained. Alternative splicing facilitates the existence of multicellular organisms because it reduces space occupied by the genes: a single gene allows the encoding of different proteins, thus enhancing the effect of exon shuffling. Splicing the exons of different primary transcripts is called trans-splicing. It can even better regulate gene expression and combine different exons to instantly obtain proteins with new functions, and is also present in organelle genes. In prokaryotes, the intron system is less represented, so the influence of introns on proteins was expressed only during evolution by horizontal gene transfer. Today, prokaryotes have a phenomenon similar to the alternative splicing: shufflon.