a) In terms of the gene pool, evolution can be defined as a generation to generation change in the allele frequencies within a population.

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1 I. Population Genetics Figure 1: Gene Pool Gene Pool: a) In terms of the gene pool, evolution can be defined as a generation to generation change in the allele frequencies within a population. Figure 2: Macroevolution vs Microevolution Microevolution:

2 a) The accumulation of changes in a population s gene pool over time leads to observable changes in the population itself, a phenomenon known a Macroevolution. II. Hardy-Weinberg Is a mathematical expression that predicts the current genotype frequencies within a population s gene pool, given the existing allele frequencies. p 2 + 2pq + q 2 = 1 p 2 = predicted frequency of homozygous dominant genotype q 2 = predicted frequency of homozygous recessive genotype pq = predicted frequency of heterozygous genotype 1 = total number of allele for a given locus Sample Problem: Albinism is a rare genetically inherited trait that is only expressed in the phenotype of homozygous recessive individuals (aa). The average human frequency of albinism in North America is only about 1/20,000. Determine the percentage of individuals who are: homozygous dominant, heterozygous carriers, & albinos. Step 1: Determine the frequency of the recessive allele q. Step 2: Determine the frequency of the dominant allele p (hint: for all traits controlled by two alleles, the frequency of the dominant allele (p) plus the frequency of the recessive allele (q) must equal 100%. Therefore, p+q=1). Step 3: Using the Hardy-Weinberg equation, determine the expected frequency of individuals who are homozygous dominant, heterozygous (carriers), & recessive (albinos). P 2 = 2pq = q 2 = *Conventionally, the homozygous recessive genotype is used to derive the frequency of the dominant allele, for its allelic makeup is known. The dominant phenotype cannot be used to generate allele frequencies unless the frequency of the homozygous dominant & heterozygous genotype are known (p = AA + ½ Aa). Hardy-Weinberg Equilibrium The HW equation predicts that the aforementioned allele & genotype frequencies will remain CONSTANT from one generation to the next (no evolution will occur) under the following set of environmental conditions: a) Infinitely Large Population Size: when the size of a population is dramatically reduced, the frequencies of alleles among the small number of individuals that remain will be much different compared to the original population = Sampling Error. b) Random Mating: assumes that all individuals mate with equal frequency. Thus all alleles within a gene pool have an equal chance of being passed on & will thus be equally represented in the next generation. c) No Mutations: prevents introduction of new alleles into a gene pool due to changes in the genetic code. d) No Migration: prevents the introduction of new alleles into or the loss of alleles from the population. e) Natural Selection: does not occur prevents certain alleles from being eliminated from a population s gene pool. As long as these conditions are met, allele frequencies will NOT change & the population is said to be in a state of Hardy-Weinberg Equilibrium for a given trait. If ANY of these conditions are violated (not maintained), allele frequencies will change leading to microevolution. The forces that can lead to changes in a population s allele frequencies include the following:

3 Hardy-Weinberg Condition Direct Microevolutionary Violation 1) Infinitely Large Population 1a) Genetic Drift 2) Random Mating 2a) Nonrandom Mating 3) No Mutations 3a) Mutation 4) No Migration 4a) Gene Flow 5) No Natural Selection 5a) Natural Selection *The net result of the direct violation of Hardy-Weinberg conditions is a change in the alleles frequencies of a gene pool, resulting in microevolution (will eventually lead to observable macroevolutionary changes) Agents of Microevolution: Violating H-W Equilibrium Figure 3: Mutations Mutation:

4 Figure 3.1: Genetic Drift Allele frequencies can change between generations due to the fact that fertilization is a random event. As a result, some alleles may get passed on in slightly greater amounts than others to cause allele frequencies to change or Drift from generation to generation. Figure 3.12: Genetic Drift Rates vs Population Size Genetic Drift: a) Events that can influence the rate of genetic drift by altering population size include Bottlenecking & the Founder Effect.

5 Figure 3.2: Influences on Genetic Drift: Bottlenecking Bottlenecking: Figure 3.3: Influences on Genetic Drift: Founder Effect Founder Effect:

6 Figure 3.4: Gene Flow Gene Flow: Figure 3.5: Nonrandom Mating Nonrandom Mating:

7 Figure 3.6: Natural Selection: Stabilizing Selection Stabilizing Selection: Figure 3.61: Natural Selection: Directional Selection Directional Selection:

8 Figure 3.62: Natural Selection: Diversifying Selection Disruptive/Diversifying Selection:

9 I. Macroevolution Figure 1: Macro vs Microevolution Generations of accumulated microevolutionary changes within the gene pool will ultimately result in macroevolution to the point of Speciation. Speciation is said to have occurred when individuals of different populations can neither: a) No longer physically mate OR b) Physically mate but not produce fertile offspring Figure 2: Interspecies Hybrids (Mules) Horse Donkey Mule 2n = 64, n = 32 2n = 62, n = 31 2n = 63 Sterile due to inability to make functional gametes. II. Pathways to Speciation Natural selection can establish new species under two distinct circumstances: a) Allopatry: promotes reproductive isolation (one of the conditions for speciation) via geographic barriers that prevent gene flow (mating) between populations. b) Sympatry: promotes reproductive isolation via behavioral differences between individuals within the same population resulting to result in a decreased likelihood of mating.

10 Figure 3: Allopatric Speciation Allopatric Speciation: Figure 4: Sympatric Speciation If some members of a population adopt different behaviors (through natural genetic variation), they may become reproductively isolated from the rest of the group (even if living among the group itself!). Such was the case involving the Hawthorn fly & Apple fly. With the introduction of apple trees to North America, some individuals of the Hawthorn fly population began to live in the apple trees instead. As a result of this preference, these individuals became reproductively isolated despite living in close proximity to the rest of the population, ultimately developing into the Apple fly species.

11 Sympatric Speciation: II. Rates of Evolution Figure 5: Gradualism vs Punctuated Equilibrium Gradualism: Punctuated Equilibrium: a) Like gradualists, evolutionists subscribing to punctuated equilibrium believe that change occurs in a gradual manner, only more rapidly in response to environmental changes. III. Systematics & Taxonomy Systematics: Taxonomy: Binomial:

12 Figure 6: Binomial Nomenclature (Common Names vs Scientific Names) Figure 7: Linnaean Classification System *This system is based on structural similarities between organisms (if they look alike, they are placed in the same group). The main problem with this is such groupings can be misleading due to the existence of ANALOGOUS STRUTURES. For example, the analogous body forms of dolphins & fish may result in them grouped together in this system despite the fact (based on molecular evidence) that they are NOT closely related.

13 Figure 8: Phylogenetic Tree Rules for reading a phylogenetic tree: 1) As you progress toward the top of the tree, you are progressing forward in time (older to more recent). 2) Each branch point on the tree represents a common ancestor to groups that arise from it. For example, x is the common ancestor to species A & B, just as y is the common ancestor to species C, D, & E. 3) The species that are closest together on the tree share the greatest number of similarities (genetic) & are thus more closely related compared to species more distantly situated about the tree. For example, species A is more closely related to species B (& vice-versa) compared to any other species.