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13. Gene and Genome Evolution.pdf

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Biology (Sci)
BIOL 200
Richard Roy

Ancestral a Tubulin (worm) Tubulin yeast A-Tubulin (human) (fly0 A Tubulin (worm) B-Tubulin (yeast) MetaboRsm Cel cell communication cytosteteenistructure DNA replication modification Protein folding and dogradation Durano and immunity Mi cellanenous function Ancestral a Tubulin (worm) Tubulin yeast A-Tubulin (human) (fly0 A Tubulin (worm) B-Tubulin (yeast) MetaboRsm Cel cell communication cytosteteenistructure DNA replication modification Protein folding and dogradation Durano and immunity Mi cellanenous functionNaveen Sooknanan McGill Fall 2011 Gene and Genome Evolution: Over evolutionary time, ancestral cells began to undergo differentiation which led to gene duplication and divergence  This is because certain changes in function need to be made by the cell because of environmental changes For example, in the tubulin gene, divergence occurred in the ancestral cell causing the gene product to change in structure and function.  This produced α and β Tubulin, both derived from one tubulin gene This new cell the underwent divergence once more in a speciation even to produce tubulin genes for two different species  α Tubulins 1 and 2 are found in species 1 and 2 respectively, and have almost the same structure and function  The same applies to β Tubulin This differentiation and speciation of an ancestral cell leads to the production of orthologous and paralogous genes  Orthologous genes are the result of a speciation event. They are almost identical in structure and function; the only difference is that they are located within different species o Orthologous genes are very informative using bioinformatics and are the easiest to compare  Paralogous genes are the result of divergence of one gene within a cell. They are different both in structure and function, but are found within the same organism o α and β Tubulin 1 are paralogous, because they are both located within the same organism o Paralogous genes are not as informative as orthologous, and can sometimes mislead us due to the fact that you must choose from 100s of related species It is evident from this graph that much of the proteins found within an organism have functions which are unknown to us  In humans, we don’t even know exactly how many proteins there are in the body There are various mechanisms involved in gene and genome evolution, the most important of which are:  Genetic reassortment  Gene and segmental duplication  Exon shuffling  Control/regulatory region diversification  Domesticated transposons 1Naveen Sooknanan McGill Fall 2011 For genetic reassortment, we will take the influenza virus as an example: The influenza virus is a very simple organism with a very small genome  It contains two materials on its outer surface: haemagglutin (H), shown in light blue, or Neuraminidase )N), shown in pink  Inside are 8 single stranded viral RNAs associated with RNA dependant RNA polymerase as ribonucleotproteins o All combined, the influenza genome is less than 10kb in length  The genome is replicated by the virus’s own RNA polymerase The influenza virus is able to evolve so quickly due to its extremely error prone RNA polymerase, which incorporates 1 mutation every 10kb; this means that every time the virus replicates, an error is introduced  The buildup of these random mutations, called antigenic shift, causes new strains of the virus to arise Furthermore, new subtypes of influenza can arise when the same host is infected by 2 or more different strains of the virus  This creates an opportunity of mixing of genomes when H and/or N vRNAs are reassorted  New strains of the virus emerge at different points in time which have caused pandemics in the past o H1N1 is the subtype of the virus which caused the Spanish flu in the 1900s, the swine flu in the 1970s and now the pandemic started in 2008 o H2N2 is what caused the Asian flu in the 1950s  There is also a possibility of species jump during this process o For example, from birds to humans, there is a virus known as the bird flu Gene and segmental duplication is a result of unequal crossing over of chromatids during replication. L1, the most common LINE in humans, could be responsible for the incorrect crossing over in this example.  Similar regions may incorrectly align with each other during alignment of sister chromatids, which, in this case, coded for the production of an extra β globin gene in the daughter organism  If the misalignment were to occur so as to eliminate the β globin gene altogether, the result
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