Môn Sinh học - Chapter 21: Genomes and their evolution

Chapter 21Genomes and Their EvolutionWhat you need to know:The major goals of the Human Genome ProjectHow prokaryotic genomes compare to eukaryotic genomes.The activity and role of transposable elements and retrotransposons.How evo-devo relates to our understanding of the evolution of genomes.The role of homeotic genes and homeoboxes.BioinformaticsUse of computers, software, and math models to process and integrate data from sequencing projectsHuman Genome ProjectPurpose: to sequence the entire human genomeCompleted in 2003Genomes sequenced thus far*: 58,000 prokaryotes, 2700 eukaryotes, 5300 viruses* Data as of 1/27/16Human Genome ProjectComparing Genomes of Bacteria, Archaea, & EukaryotesHuman DNA3 billion base pairs~20,000 genesOnly 1.5% codes for proteins (or RNA)Mostly Repetitive DNA: sequences present in multiple copiesVideo Clip:What are SNPs?Transposable ElementsMake up 75% of repetitive DNAStretches of DNA that can be moved from one location to another in genomeDiscovered by Barbara McClintock – corn breeding experiments2 Types:TransposonsRetrotransposonsTransposonsMoves within genome via DNA intermediate“cut & paste” or “copy & paste” mechanismsRequires enzyme transposaseRetrotransposonsMove by means of RNA intermediateLeaves copy at original siteInvolves enzyme reverse transcriptaseGenome EvolutionInsertion effects of transposons:Can interrupt or alter gene functionMultiple copies of genesDuplication  genes with related functionsGenes diverge by accumulating mutationsSome become nonfunctional pseudogenesEventually, new genes with new functions can occurMultigene FamiliesCollections of 2 or more identical or very similar genesEg. hemoglobin: -globin and -globin gene familiesTranspositions  chromosomal rearrangementsTransposable elements contribute to evolutionPromote recombination, disrupt genes or control elements, & carry genes to new locationsMay be harmful or lethal, but can also have small beneficial effectsProvides raw material for natural selectionHHMI Short Film:The Birth & Death of GenesIllustrative Example: Antifreeze Gene in FishAntifreeze proteins (AFP): produced by vertebrates, plants, fungi, bacteria to aid survival in sub-zero environmentsFunction: bind to ice crystals and prevent growthAntarctic fish: old protein gene transformed into a new gene with new structure/functionGene mutates  duplicated  divergent evolution Evolutionary Development(Evo-devo)Compares developmental processes to understand how changes can lead to evolution of organismsHomeotic genes: master regulatory genesControl placement and spatial organization of body partsHomeobox: widely conserved 180-nucleotide sequence within homeotic (Hox) genesFound in many groups (fungi, animals, plants)Hints at relatedness between all life formsConservation of homeotic genes