XI.7 Genes consist of exon and intron areas

The modular structure of genes is a very obvious property, especially in genes encoding the proteins of eukaryotic organisms (Gilbert 1978).DNA sections encoding a certain protein are interrupted in many places by DNA sections, called introns, that do not encode the protein and that must be spliced off before translation of RNA into a sequence of aminoacids.Short genes with a length to about 500 pairs usually do not contain introns; however, in longer genes, the content of introns first increases very rapidly and then slowly with the length of the gene (Fig. XI.5).The process of excising of introns from pre-mRNA and reconnection of the remaining parts, called exons, in a continuous chain of functional mRNA, is called RNA splicing.Because there are several completely different mechanisms of splicing of introns (Belfort 1993), it is probable that splicing originated repeatedly and possibly even independently during the process of evolution of modern organisms.s

            The existence of introns poses two fundamental questions for biologists.Did introns exist in genes from their origin or were they subsequently inserted in these genes?What is the functional importance of the presence of introns; why do organisms not get rid of them during evolution?

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.