Lecture_6_Molecular_Evolution

Lecture_6_Molecular_Evolution - 6/15/2011 Genomes Molecular...

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6/15/2011 1 Molecular Evolution LS1: Summer Session A July 1, 2011 Genomes The entire complement of an organisms DNA is called its genome A genome includes protein coding genes as well as non-coding regions The genome is a comprehensive, interacting unit including genes arrayed in sequence, regulatory regions, and structural elements Genomic studies permit an understanding the evolutionary relationships as well as the processes underlying the evolution of genes Molecular Evolution The field of molecular evolution examines: The relationships between genes and protein function Evolutionary history of genes Variations in genome size and composition Central to the task of molecular evolution is the identification and alignment of homologous sequences Sequence alignment Recall that similarities in DNA or protein sequences can be used as evidence of common ancestry (homology) Sequence alignment is the comparison of two or more DNA or protein sequences From these data, a similarity matrix can be made Sequence alignment Similarity matrix
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6/15/2011 2 Reconstructing evolutionary history Sequence alignments and similarity matrices can be used as characters to reconstruct phylogenetic histories But many more inferences about evolutionary history can be made with such data Times of divergence The number of differences between lineages provides an indication of the time of divergence between them The changes provide a minimum estimate of divergence times Actual substitution rates are higher due to: Multiple substitutions Coincident substitutions Parallel substitutions Back substitutions Correcting for substitution rates Mathematical algorithms can help to correct for the underestimation of gross differences between two sequences: Transition/transversion substitution rate Variable rates of substitutions across a gene Different nucleotide compositions Corrections can estimate the true divergence times between organisms Comparisons between multiple
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This note was uploaded on 09/08/2011 for the course LS 1 taught by Professor Thomas during the Summer '05 term at UCLA.

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Lecture_6_Molecular_Evolution - 6/15/2011 Genomes Molecular...

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