MICROEVOLUTION VS. MACROEVOLUTION • Microevolution: survival through the inheritance of favorable characteristics – mutations – selection • Macroevolution: progression of biodiversity through geological time – speciation – extinction MICROEVOLUTION Evolutionary Mechanisms Types of Natural Selection Hardy-Weinberg Equilibrium WHAT IS MICROEVOLUTION? • Traces generational changes in a population of organisms • Changes eh? – Allelic frequency changes within a gene pool! • WHAT LEADS TO CHANGES IN THE GENE POOL OF A POPULATION? • SMALL POPULATION SIZE (small pop frequencies) toss a coin to prove it. MECHANISMS OF EVOLUTION • GENETIC DRIFT (random/chance events that change the gene pool of a small population) examples: natural disasters 2 TYPES OF GENETIC DRIFT MECHANISMS • Genetic Bottleneck dramatic decrease in pop size due to : catastrophes predation disease, etc. • Founder Effect migration leads to changes in allele frequencies from population of origin WHAT ELSE CAUSES GENE POOL CHANGES ? • GENE FLOW immigration emigration EX OF GENE FLOW IN HUMANS • Frequency of Rh- allele among Africans: 63% • Frequency of Rh- allele among African-Americans 45% • Frequency of Rh- allele among White European population • MUTATIONS may produce a selective advantage may produce deleterious effects may be harmless • NATURAL SELECTION! increases/decreases allele frequencies due to environmental impact. Ex: English Peppered Moths • NON-RANDOM MATING individuals choose based upon traits (vertebrates) individuals “choose” based upon physical proximity (invertebrates) OTHER FORMS OF NONRANDOM MATING: • INBREEDING – Proximity issues • SEXUAL SELECTION: 1. Male competition: # offspring fitness 2. Female choice: quality offspring fitness SEXUAL SELECTION Picky females, show-off males… MICROEVOLUTION REVIEW • Changes in the GENE POOL! • Caused by: – Gene Flow – Natural Selection – Mutations – Non-Random Mating • Sexual Selection • Inbreeding THE SIGNIFICANCE OF SELECTION • Selection increases the adaptive qualities of a population for the environment in which it lives. Types of Selection: Natural Selection determined by phenotype selection toward phenotypes that improve fitness SUBDIVISIONS OF NATURAL SELECTION… Stabilizing Selection Eliminates individuals with extreme traits. Results in decreased variation Directional Selection Favors traits at ONE extreme ex: resistance to insecticides DIRECTIONAL SELECTION Disruptive Selection Selection toward BOTH extremes. Extreme traits are favored, common traits are NOT! Results in major divisions in population! What might result? DISRUPTIVE SELECTION ARTIFICIAL SELECTION Directional selection determined by humans CAUSES OF VARIATION • Mutation is the ultimate source of variation • Two major types of mutations: –Gene mutations –Chromosome mutations GENE MUTATIONS Addition / Insertion Deletion Substitution Inversion SPECIFIC EXAMPLES OF MUTATIONS • Gene mutations –PKU (phenylketonuria) –CF (cystic fibrosis) • Chromosome mutation –Klinefelter syndrome (male with 47,XXY karyotype) ONCE MUTATIONS HAVE ARISEN, FURTHER VARIATION RESULTS FROM: • Recombination of alleles during meiosis • Recombination of alleles during ONCE GENETIC VARIATION HAS ARISEN, THERE IS ALSO PHENOTYPIC VARIATION. • Recall that, according to Darwin’s Theory, due to competition within populations, there is … Differential Reproduction GREAT EXAMPLE OF DIFFERENTIAL REPRODUCTION OF SELECTED PHENOTYPES: ULTIMATE RESULT OF EVOLUTION Change in the genetic composition (gene pool) of a population. RELATED CAUSES OF GENETIC VARIATION Sexual Reproduction! • Diploidy • Outbreeding MINORITY ADVANTAGE… • 50/50 Sex Ratio • Predation (more common phenotype preferred by predator) • The Lefty Hypothesis 10-15 % general population >50% contact sports (esp. males) REPRODUCTIVE ISOLATION Prezygotic • Temporal isolation • Behavioral isolation • Mechanical isolation • Ecological Postzygotic • Hybrid inviability • Hybrid sterility • Hybrid breakdown ALLOPATRIC SPECIATION SYMPATRIC SPECIATION GRADUALISM Species A evolves to become species B. LONG, GRADUAL process! PUNCTUATED EQUILIBRIUM • Evolution is Slow with brief periods of rapid development of new species. THE HARDY WEINBERG LAW • If allele frequencies for a population do not change… NO EVOLUTION IS OCCURRING! • Genetic Equilibrium • Hardy Weinberg Equilibrium GENETIC EQUILIBRIUM OCCURS ONLY IF THERE IS… 1.A large breeding population 2.Random mating 3.No change in allelic frequency due to mutation 4.No immigration or emigration EQUILIBRIUM REQUIRES… • Large Population Size (laws of probability must apply) • Isolation of Population (no immigration/emigration to/from other populations) • NO MUTATIONS ALLOWED! • NO NATURAL SELECTION ! all traits must be selectively neutral • Mating Must Be RANDOM equal probabilities of mating btwn IS HW EQUILIBRIUM POSSIBLE? • YES ? / NO ? • WHY / WHY NOT?? • http://zoology.okstate.edu/zoo_lrc/biol1114 /tutorials/Flash/life4e_15-6-OSU.swf THE HARDY-WEINBERG EQUATION • Given one locus with two alleles (A,a) the frequency of either allele is described by a number from zero to one: allele absent from pop freq = 0 same allele in all indiv in pop freq = 1 WHAT IF BOTH ALLELES ARE PRESENT IN A POPULATION? • Frequency of both alleles is equal to p+q=1 [p = dominant allele (A)] [q = recessive allele (a)] • Knowing the frequency of one allele allows for the calculation of the other… p = 1- q ; q = 1 - p • If p+q=1, then (p+q)2 = 1. Expand it and get… p 2 + 2pq + 2 q = 1 WHAT DOES IT ALL MEAN GENOTYPICALLY? p2 = frequency of AA 2pq = frequency of Aa q2 = frequency of aa PROBLEM 1 • In pigs, the allele for black coat (b) is recessive to the allele for pink coat (B). WHAT % OF PIGS ARE HETEROZYGOUS FOR PINK COAT? PROBLEM 2 In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? PROBLEM 3 Phenylketonuria (PKU) is a human metabolic disorder that results in mental retardation if it is untreated in infancy. In the United States, one out of approximately 10,000 babies is born with the disorder. Approximately what percent of the population are heterozygous carriers of the recessive PKU allele? POPULATION IS BORN WITH A SEVERE FORM OF SICKLE-CELL ANEMIA (SS), WHAT PERCENTAGE OF THE POPULATION WILL BE MORE RESISTANT TO MALARIA BECAUSE THEY ARE HETEROZYGOUS(SS) FOR THE SICKLE-CELL GENE?