MIT6_047f08_lec16_note16

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 6.047 / 6.878 Computational Biology: Genomes, Networks, Evolution Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . Comparative Genomics II: From Genomes to Evolution Lecture: Manolis Kellis. November 4, 2008 1 Introduction This is the second lecture in a series of two lectures on the work being done in Prof. Kelliss lab on comparative genomics. Comparing genomes of related species at different evolutionary distances can teach us both about the genetic code and about evolution. In this lecture we discussed two examples of what we can learn about evolution using comparative genomics. The topics of this lecture are discussed in greater detail in the papers [1] and [2]. A brief summary is given in these notes with references to figures in lecture slides. 2 Whole genome duplication Evolution requires infrequent random errors, i.e. mutations, in cell division to create variation in different species. Genomic duplication is a particular type of such error which can be useful to explain innovations in evolution[3]. Most of the time genomic duplication will lead the daughter cell to be less fit (sick) and to get selected out. However, if the daughter species survives and adapts, one copy of an original gene can perform its task while the other gene can evolve to gain new function increasing gene content and fitness. In class, we discussed one type of genomic duplication, namely whole genome duplication (WGD), in the study of which comparative genomics has brought in novel information. 2.1 Before comparative genomics In his 1970 book Evolution by Gene Duplication where he postulated the role of genomic duplication in evolution, Ohno also suggested the occurance of whole genome duplications, in particular that the vertebrate genome is the result of one or more whole genome duplications[3]. Such large scale duplications would explain, for example, how there are 4 Hox genes in humans compared to 1 Hox gene in ies. 1 WGD has been suggested in various other cases but conclusive evidence was not found until 2004. In particular, the possibilty of WGD in the yeast S. cere- visiae has been debated since 1997. When S. cerevisiae genome was sequenced, large duplication blocks were observed. Wolfe and colleagues suggested that these duplications were due to a WGD[4]. Others have argued that the ob- served paralogous gene rate of 8% was too small to suggest a WGD and could be explained with independant local duplications[5]....
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