Gene duplication is a minimalist version of repetitive DNA (figures 10.1-10.3, pgs. 257-259). Many genes in the genome are duplicated and when this happens one of the copies may be "freed" from constraints and evolve a new function. The best understood case of this phenomenon is the evolution of the globin genes myoglobin, α-hemoglobin, ß-hemoglobin. The existence of duplicated genes forces us to recognize different kinds of homology because there are two ways to have a common ancestor: by gene duplication and by speciation . When two genes share a common ancestor due to a duplication event we call them paralogous ( α-hemoglobin and ß-hemoglobin in you are paralogous as are the α-hemoglobin in you and the ß-hemoglobin in chimps). When two genes share a common ancestor due to a speciation event we call them orthologous ( α-hemoglobin in you and α-hemoglobin in chimps). Obviously when constructing a cladogram from molecular data one should use orthologous genes if one wants to build a tree of organisms
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This note was uploaded on 11/05/2011 for the course BIOLOGY MCB2010 taught by Professor Jessicadigirolamo during the Fall '10 term at Broward College.