Chapter 9How Genes and Genomes Evolve“Nothing in biology makes sense except in the light of evolution”- Theodosius DobzhanskyExam Tuesday (next class period)This is key to understanding-evolution- emerging new viruses, and knowing that new viruses will emerge and threaten us- development of antibiotic resistant bacterial strains- appearance of herbicide resistance, and new plant and crop pathogens- appearance of new traits in viruses, bacteria, plants, and animalsObjective: Understand the basic mechanisms of evolutionarychangeBe#able#to:• Explain the difference between somatic cells and germ linecells, and the consequences of mutations in the two cell types• Discuss 5 basic types of mutations• Explain neutral mutations• Explain an origin of gene families• Explain how you could infer recent versus ancient duplications• Diagram an unequal crossover• Diagram a transposon copying an exon from one gene toanother gene• Diagram plasmid transfer between 2 bacteria• say the size of the human genome, and the rough percentagethat encodes proteins• find an open reading frame in a genomic sequence• predict evolutionary relationships by comparing DNAsequencesGametes and Somatic Cells have Distinct FunctionsStem cells have the potential to differentiate into many different cell typesMutations in gametes and somatic cells have distinct consequences09_03_altered.genes_part1.jpgFive basic types of genetic change that contribute to evolution1234(Followed by deletion ordivergence)09_03_altered.genes_part2.jpgFive basic types of genetic change that contribute toevolution, cont.5Much more common in prokaryotes than eukaryotes; majorproblem with development of antibiotic resistancePoint mutations or small insertion/deletions are primarily due toerrors in DNA replication or repairOnly a small percentage of genomic DNA encodes proteinsor regulatory sites. If a mutation does not cause a change ina protein sequence or gene regulation it is usuallyselectively neutral.Neutral (silent) mutations can accumulate at a steady rateand can be useful for estimating evolutionary relationships.Many genes belong to gene families, even in simple prokaryotesUnequal crossing-over can lead to gene duplicationThe duplicated copy accumulates mutations at a much higher rateThe copy can be lost, become a pseudogene, or evolve a differentfunction.Inferred sequence ofevents leading to thehemoglobin genefamily in vertebratesOccasionally, an organism’s wholegenome can be duplicated. This isvery rare in vertebrates, but verycommon in plants.Many crops are polyploid. Cotton,tobacco, and soybean are alltetraploid, rather than diploid.09_10_Exon.shuffling.jpgMany eukaryotic genes appear to be the result of exon shufflingNovel combinations ofprotein domainsWhat processes could mediate exon shuffling?Exons can be duplicated or shuffled by unequal crossingover within introns09_11_exon.arrange.jpgTransposable elements can affect genes they insert into09_12_Mutation.jpgHere, a transposable element has activated genes for making legsin the area where antennae would normally develop.Mutants with one organ in the place where another should beare called homeotic mutants.Horizontal gene transfer in bacteria through conjugationallows transfer of plasmids or even whole chromosomes.Horizontal transfer is rare in eukaryotes today, but itmay have been more common in the distant past.09_26_noncoding.jpgThe vast majority of the human genome does not encode proteins09_27_Computer.prog.jpgThe human genome is almost completely sequenced, but findinggenes in a sea of apparent nonsense is challenging.09_19_human_mouse1.jpgMutations accumulate faster in non-coding regionsAre non-coding regions mutated more frequently?mousehumanComparative genomicsLarge amounts of whole-genome sequence information is nowavailable representing a wide range of organisms.Comparison and contrast of sequence data allow inferences tobe made regarding evolutionHomologous genes: genes that have similar sequence becausethey share a common ancestry. The more similar the morerecently diverged.Genetic drift: divergence due to random mutationPurifying selection: conservation of sequence due to the loss ofindividuals that carry mutations in important genesSynteny: conserved gene content, order and orientation betweenchromosomes of different species09_15_Phylogen.trees.jpgInferring ancestry from a current genePrimate chromosomes havesynteny.Synteny is reduced whencomparing human to mousechromosomes but those regionsthat remain similar are likely tohave been maintained due topurifying selection09_18_transposons.jpgMany regions of the human genome have genesarranged in the same order as the mouse genome.Human MouseThe Tree of Life is constructed by comparing DNA sequences ofhighly conserved genes, especially ribosomal RNA genes.09_23_tree.of.life.jpgUseful text
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