Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28MeiosisSlide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Genetics for HumanEvolutionWhere do we come from?Have life forms changed?Creationism: the world and everything in itwas created divinely all at once, and life formsare immutable (don’t change).By end of 1700s accepted that life forms hadchanged – but by what mechanism(s)?Inheritance of acquired characteristics:During lifetime of an individual, changes occur that are passed on to an offspring.X Discounted Xhttp://shirts.meetees.com/CHARLES.htmlPicture added byErica ShofnerNatural selection: • Organisms are adapted to their environment;• Variation already exists among a population; • Population undergoes adaptive change when the environment changes:HOW?• Those members of the population best adapted will survive.• Those who survive pass on their variation to the next generation.There is no direction to evolution. Organisms change as a result of natural selection through survival of the fittest.Environment of todayDistribution of variation in populationEnvironment changesNow only the humans with these variations can surviveThese humansdie beforereproducingIn the next generation thedistribution of variation inthe population changesTheory of Natural Selection formulated byCharles Darwin and Alfred Russell WallaceWallace published first, but Darwin had thought ofnatural selection 20 years before but was afraid topublish.Charles Darwin, 1859On the Origin of Species by Means of Natural Selection The entire first edition of 1,250 copies was sold out the first day it appeared. www.smh.com.auDarwin was naturalist on voyages of HMS Beagle 1831-1836Convinced him of natural selection rather than divine creation.In his Autobiography, he says he finally wrote an abstract of this theory in 1842, and he enlarged it in 1844. In 1844 he wrote to J. D. Hooker (a famous botanist): “At last the gleams of light have come, and I am almost convinced (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable.”Darwin and Wallacedidn’t know the mechanisms by which variationwas present in populations – our understanding of genetics is based on work by Gregor Mendel in 1866but not rediscovered until 1900Darwin vs. LamarkKey difference in the two theories•Inheritance of acquired traits (Lamark)- variation arises when needed •Natural selection (Darwin) – variation already exists and nature selects those variations that are best suited to the current environmentOVERVIEW1. There has been change through time in organisms and in geology.2. This change has not been directional.3. Biological change through natural selection.Theory of Natural Selection 5 main points to remember:1. Organisms are adapted to their environment2. Variation already exists within the population3. Population undergoes adaptive change when environment changesWhy evolve when the environment changes?4. Those best adapted to new environment survive5. Those who survive pass on their variation to their offspringClassic example: The Peppered MothSlide by Erica ShofnerToday we’ll talk about these last two points: What is the source of variation, and How is that variation passed on to offspring?Let me point out right now that in talkingabout evolution, we must talk ultimatelyabout populations, not individuals. . . But we need to start by talking aboutindividuals resulting from sexual reproductionMendel discovered that inheritance ofcharacteristics is particulate (rather thanby blending) – traits are controlledseparately by individual particles calledgenes.In 1953 Watson and Crick discoveredthat genes are portions of DNA moleculesA gene is a chemical code or blueprint for producinga protein, some of which make up the basic structure of a cell in the form of enzymes.Each genetic code is made up of a sequence of bases that are part of a chemical strand called DNA.There are only four bases, called by their firstinitials, A, T, C, and GBases are arranged in groups of three, calleda codon.Each codon makes an amino acidA chain of amino acids supplies the blueprint fora proteinHumans can produce at least 100,000 different proteins!codonmakesan amino acidcodonmakesan amino acidchain of codonssupplies blueprintfor making a proteinTaken from: Human Genome Program, U.S. Department of Energy,Genomics and Its Impact on Science and Society: A 2003 Primer, 2003.A gene is a segment of DNA that dictates the sequence of amino acids to form a particular proteinA specific gene is located in a specific location or locus on the DNA strand. locus – singularloci - plural•A cell has a nucleus •Within the nucleus is DNA•DNA is made up of four bases: A, T, G, C•A series of three bases makes up a codon•Each codon makes an amino acid•A group of codons makes a gene, which makes a protein•A gene has a particular locus or location on the DNA strand (or chromosome) and directs the development of certain traitsSlide by Erica ShofnerRecapMost of the time, DNA exists uncoiled in the cell’s nucleusHowever, during cell division, DNA becomes tightly coiled into chromosomesEach species has a characteristicnumber of chromosomes: Humans have 46, in 23 pairsBeing in pairs is called diploidChromosome pairs split during meiosis, or duringformation of the sex cells, resulting in an offspringreceiving half their genetic material fromeach parent, or the haploid number of chromosomes.Haploid refers to being singleThe number of chromosomes you haveis not related to how complex you are . . .Humans have 46 chromosomesGoldfish have 94Brine shrimp have 320!A cabbage has 18GenomeThe total genetic endowment of an organismBy 2003, the entire human genome had beenstudied for two humans98% of the genome is not composed of genesthat code for proteins: It is noncoding DNA.We are still learning the functions of thisnoncoding DNA and still trying to figure outthe loci of the genesAs we mentioned, a gene has a particular locus on a chromosome (tightly wrapped DNA)Variations of a particular gene at specific loci are called alleles. Alleles direct a cell to make slightly different forms of the same protein. So an allele results from a change in the codons!Different alleles can cause different expression of a
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