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Bio1020, Diversity of Life: January 31.docx

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University of Lethbridge
BIOL 1020
Robert Laird

January 31, 2014 – Biology Genes, molecular clocks and evolution Molecular systematics: • DNA sequences can provide derived homologies just like morphological traits can. Genes present due to shared ancestry o Use of DNA in systematics: rates of molecular evolution differ within and between lineages o DNA that codes for rRNA evolves slowly: used for determining relationship between taxa that diverged long ago (100s of millions of years). rRNA not good for short time changes. o mtDNA evolves relatively rapidly: useful for determining relationships between taxa that diverged comparatively recently (1000s of years), recent speciation. • Their use is revolutionizing systematics • Allows comparison of groups that have little in common morphologically (fungi and animals) • Allows reconstruction of phylogenies for limited/non-existent fossil records (soft-bodied organisms) • Gene duplication and gene families o Gene duplication increases the number of genes in the genome, providing more opportunities for evolutionary changes o Repeated gene duplications result in gene families o Type of homologous genes, duplicated genes can be traced to a common ancestor o Figure 26.18: good way to determine speciation  Orthologous genes: a product of speciation • Widespread and extend across • Gene number and the complexity of an organism are not strongly linked • Genes in complex organisms appear to be very versatile: some genes can perform many functions  Paralogous genes: within a species • Genes for myoglobin and hemoglobin • Functional redundancy: multiple copies, if one goes wrong there is a BACKUP! • Evolution of new functions: two copies of a gene, start evolves independently from eachother, mutations, o Humans, mice, fruitflies, yeast: among other model organiasms, mice, fruitflies, and yeast are importan for medical genetics research  Homologous (orthologous) genes  Biochemical pathways  Developmental pathways Molecular clocks • Purpose: to put an absolute time scale of divergence t
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