Genetics for Human Evolution Where do we come from Have life forms changed Creationism the world and everything in it was created divinely all at once and life forms are immutable don t change By end of 1700s accepted that life forms had changed 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 X Picture added by Erica Shofner http shirts meetees com CHARLES html Natural 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 today Distribution of variation in population Environment changes These humans die before reproducing Now only the humans with these variations can survive In the next generation the distribution of variation in the population changes Theory of Natural Selection formulated by Charles Darwin and Alfred Russell Wallace Wallace published first but Darwin had thought of natural selection 20 years before but was afraid to publish Charles Darwin 1859 On 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 au Darwin was naturalist on voyages of HMS Beagle 1831 1836 Convinced 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 Wallace didn t know the mechanisms by which variation was present in populations our understanding of genetics is based on work by Gregor Mendel in 1866 but not rediscovered until 1900 Darwin vs Lamark Key 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 environment OVERVIEW 1 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 environment 2 Variation already exists within the population 3 Population undergoes adaptive change when environment changes Why evolve when the environment changes 4 Those best adapted to new environment survive 5 Those who survive pass on their variation to their offspring Classic example The Peppered Moth Slide by Erica Shofner Today 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 talking about evolution we must talk ultimately about populations not individuals But we need to start by talking about individuals resulting from sexual reproduction Mendel discovered that inheritance of characteristics is particulate rather than by blending traits are controlled separately by individual particles called genes In 1953 Watson and Crick discovered that genes are portions of DNA molecules A gene is a chemical code or blueprint for producing a 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 first initials A T C and G Bases are arranged in groups of three called a codon Each codon makes an amino acid A chain of amino acids supplies the blueprint for a protein Humans can produce at least 100 000 different proteins codon makes an amino acid codon makes an amino acid chain of codons supplies blueprint for making a protein Taken 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 protein A specific gene is located in a specific location or locus on the DNA strand locus singular loci plural Recap 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 traits Slide by Erica Shofner Most of the time DNA exists uncoiled in the cell s nucleus However during cell division DNA becomes tightly coiled into chromosomes Each species has a characteristic number of chromosomes Humans have 46 in 23 pairs Being in pairs is called diploid Chromosome pairs split during meiosis or during formation of the sex cells resulting in an offspring receiving half their genetic material from each parent or the haploid number of chromosomes Haploid refers to being single The number of chromosomes you have is not related to how complex you are Humans have 46 chromosomes Goldfish have 94 Brine shrimp have 320 A cabbage has 18 Genome The total genetic endowment of an organism By 2003 the entire human genome had been studied for two humans 98 of the genome is not composed of genes that code for proteins It is noncoding DNA We are still learning the functions of this noncoding DNA and still trying to figure out the loci of the genes Like chromosomes genetic loci also come in pairs As 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 trait Where does a different allele come from Mutation A random change in a gene Pair of alleles Lewis Jurmain and Kilgore 2008 Understanding Physical Anthropology and Archaeology p 49 In sexual reproduction the organism produces special sex cells or gametes To do so a cell passes through meiosis which splits the chromosome pairs and
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