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Molecular Evolution



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Molecular Evolution Gene Duplication Gene duplication Gene duplication is a primary means by which new genes can arise Dr Erica Bree Rosenblum Gene duplication Types of gene duplication 1 2 3 4 5 Partial internal internal gene duplication Complete gene duplication Partial chromosomal duplication Complete chromosomal duplication Whole genome duplication Exon duplication Gene duplication Principle mechanism for gene duplication is unequal crossing over Unequal crossing over is facilitated by repetitive sequences So gene duplications particularly those in tandem can beget more duplications Exon duplication Eukaryotic genes contain many exons Exon duplication can be advantageous by Neighboring exons are often very similar suggesting history of exon duplications a Enhancing number of functional or structural domains so the protein can perform existing functions better faster Exon duplication is major mechanism for gene elongation and evolution of complexity b Decreasing constraint on one exon copy allowing development of new functions 1 Exon duplication Example antifreeze genes in fish Freezing of Antarctic ocean 10 14 MYA Antifreeze glycoprotein gene 5 14 MYA Many duplication events in short time period likely under strong positive selection Exonization Exons can appear and disappear in processes other than shuffling Exonization process by which intronic sequence become exons not very common Pseudoexonization process by which exon not whole gene becomes nonfunctional Gene duplication Gene duplication can result in a copy that a becomes a functionless pseudogene most duplicate genes have a half life of only a few million years b retains its original function these invariant repeats can enable dose effects by allowing more protein production c develop a novel function these variant repeats can create new genes via neofunctionalization Exon shuffling Exon shuffling can arise from duplication insertion or deletion Insertion of exons from one gene into another can create



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