Lecture 4•A population’s genetic structure includes its “allele frequency” and “genotype frequency”.“Frequency” is the proportion - the relative number - usually expressed as a decimal, e.g., 0.4•With normal meiosis and random fertilization, there is no change in allele frequency from generation to generation. Mendelian inheritance, by itself, maintains genetic equilibrium.Some Relevant Definitions: (review: what is an allele? what is a genotype?)•Gene pool: the set of all copies of alleles carried by individuals in a population at one time•Allele frequency: the proportion of a certain allele at a given locus within a population•Genotype frequency: within a population the proportion of a given genotype (of 3 possible genotypes in a two-allele system: e.g., two homozygous genotypes and the heterozygote)•Microevolution: the change in allele frequencies in a population over time (not genetic equilibrium)•Hardy-Weinberg equilibrium: equilibrium situation in which allele and genotype frequencies do not change from one generation to the next, so no evolution is occurring for genes at that particular gene locus.Calculate Allele frequencies and Genotype frequencies:Let "p" stand for the frequency of one allele, e.g., dominant or wild-type (2-allele system, simple dominance)Let "q" stand for the frequency of the other (recessive) allele, then A(p) a(q)p + q = 1 is the equation for allele frequencies A(p) AA(p2) Aa (pq)By mapping allele frequencies onto a Punnett Square, a(q) Aa (pq) aa (q2)under conditions of genetic equilibrium, we predict possible genotype frequencies in the next generation.Hardy-Weinberg equation: p2 + 2pq + q2 = 1p2 = freq. of homozygous dominants; 2pq = freq. of heterozygotes; q2= freq of homozygous recessivesSo the full Hardy-Weinberg equation is the equation for genotype frequenciesConditions of Hardy-Weinberg equilibrium: Five assumptions: (a) large population size, so less effect of chance events, (b) no gene flow into/out of a population or between populations, (c) mutations not significant, (d) random mating, and (e) no natural selection, [diploid, sexually-reproducing organisms.]•When one or more conditions of H-W equilibrium is not met, the allele frequency and/or genotype frequency can change from generation to generation. That is, microevolution can occur.•Although most populations are not in H-W equilibrium for all traits (why not?), the H-W equation is very useful for quantifying allele frequencies & genotype frequencies in the gene pool and predicting change.Learning Objectives: [after you understand allele and genotype frequencies]1-32. Explain why genetic variation within a population is a prerequisite for evolution. (CC 23.1 #1)Genetic variation within a population is a prerequisite for evolution because natural selection is the primary mechanism for change. Individuals differ in their inherited traits and that selection acted on such differences, leading to evolutionary change. Darwin’s finches helped him lead to this conclusion.1-33. Name the five main assumptions of Hardy-Weinberg equilibrium. Explain how violating any one of those assumptions would cause the population (gene pool) to evolve and not stay in equilibrium.(a) Large population size, so less effect of chance events(b) No gene flow into/out of a population or between populations(c) Mutations not significant(d) Random mating(e) No natural selection, [diploid, sexually-reproducing organisms.]•When one or more conditions of H-W equilibrium is not met, the allele frequency and/or genotype frequency can change from generation to generation. That is, microevolution can occur.1-34. Distinguish between these two examples of genetic drift: bottleneck effect and founder effect.Bottleneck effect: Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.Founder effect: Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.1-35. Distinguish between “gene flow” and “genetic drift”. Tell how you would ‘act these out’ with M&M’s.Gene flow: The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes  a few random M&Ms move to another M&M populationGenetic drift: A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects of genetic drift are most pronounced in small populations.  an example of a bottleneck effect: as the M&Ms are being poured out from the container, one allele could be more presentLecture 51-36. Explain how evolution can occur in the absence of any type of selection (no natural/artificial selection).Mutation and Sexual Reproduction -Mutation: from environment & surroundings -Reproduction: the unique combination of alleles that each individual receives.Gene flow and genetic drift: occurs by chance bottleneck, founder effect; alleles being randomly introduced into a populationNon-random Mating: inbreeding can cause an increase in a dominant trait; by chance sperm could travel to many eggs within that population1-37. Define “adaptation”. (See glossary) How does the process of natural selection produce adaptations?Adaptation: inherited characteristic of an organism that enhances its survival and reproduction in a specific environment. Natural selection consistently increases the frequencies of alleles that provide reproductive advantage and thus leads to adaptive evolution.1-38. What is “relative fitness”? In what way is the phrase "evolution is survival of the fittest" misleading?Relative fitness: the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.“Evolution is survival of the fittest “ is misleading because although there are animal species in which individuals, usually the males, lock horns or otherwise do combat to determine mating privileges but reproductive success is generally subtler and depends on many factors besides outright battle. For example, a barnacle that is more efficient at collecting food than its neighbor may have greater stores of energy and hence be able to produce a larger number of eggs.1-39.