BIOL 1070 | UNIT 2: EVOLUTION

LEC 1 - FEB 10

Definition of Evolution

• Evolution is the process that results in changes in the proportion of heritable traits within populations from one generation to the next.

• Codon learning definition: defined as a change in allele frequencies in a population.

• Includes four forces/mechanisms that drive these changes: All four are simultaneously and continuously acting on every population of living organisms.

  1. Natural Selection

  2. Mutation

  3. Genetic Drift

  4. Gene flow

Natural Selection

• Only mechanism leading to adaptations.

• Adaptations:

  • Heritable traits enhancing fit between organism and environment.

  • Aid in survival and reproduction.

• Grant Research

  • Peter and Rosemary Grant: prominent evolutionary biologists.

  • Researching finch population on Daphne Island since 1973.

    Science and Religion

    • Distinction between science and religion

      • Science investigates the natural world

      • Religion addresses the spiritual and supernatural

      • Both can coexist, but supernatural explanations are outside the realm of science

      • Class focus: Scientific hypotheses and testing

    Science and Religion

    • Distinction between science and religion

      • Science investigates the natural world

      • Religion addresses the spiritual and supernatural

      • Both can coexist, but supernatural explanations are outside the realm of science

      • Class focus: Scientific hypotheses and testingScience and Religion

        • Distinction between science and religion

          • Science investigates the natural world

          • Religion addresses the spiritual and supernatural

          • Both can coexist, but supernatural explanations are outside the realm of science

          • Class focus: Scientific hypotheses and testing

  Medium Ground Finches

  • One of two finch species on Daphne Island.

  • Characterized by stubby beaks; primarily seed-eaters.

  • The Grants monitored these finches on the island.

Science and Religion

• Distinction between science and religion

  • Science investigates the natural world

  • Religion addresses the spiritual and supernatural

  • Both can coexist, but supernatural explanations are outside the realm of science

  • Class focus: Scientific hypotheses and testing

IC 1: D

IC 2: A,B,E

IC 3: B

Evolution in Context

• Succinct definition of evolution: A change in allele frequencies within a population

Page 9: Mechanisms of Evolution

• Four mechanisms that drive evolutionary change:

  1. Natural Selection

  2. Mutation

  3. Genetic Drift

  4. Gene Flow

• All mechanisms act concurrently on every living population

Natural Selection

• Key evolutionary mechanism for adaptations

  • Adaptations: Heritable traits enhancing survival and reproduction

  • Evolution in Context

    • Succinct definition of evolution: A change in allele frequencies within a population

    The Grants

    • Researchers: Peter and Rosemary Grant

      • Focused on finch populations on Daphne Island since 1973

    Page 13: Medium Ground Finches

    • Description of a finch species on Daphne Island

      • Characterized by stubby beaks

      • Primarily consume seeds

      • Grants tracked the population's changes over time

    Page 14: Beak Depth Variation

    • Functional adaptation:

      • Deeper beaks are advantageous for accessing large/hard seeds

      • Comparison between deeper and shallower beaks

    Page 15: The 1976 Drought

    • Significant drought event lasting 551 days

      • Resulted in shifts in seed availability

      • Prior data on finch population existence before and after drought analysis

    Page 9: Mechanisms of Evolution

    • Four mechanisms that drive evolutionary change:

      1. Natural Selection

      2. Mutation

      3. Genetic Drift

      4. Gene Flow

    • All mechanisms act concurrently on every living population

    Page 10: Natural Selection

    • Key evolutionary mechanism for adaptations

      • Adaptations: Heritable traits enhancing survival and reproductionEvolution in Context

        • Succinct definition of evolution: A change in allele frequencies within a population

        Page 9: Mechanisms of Evolution

        • Four mechanisms that drive evolutionary change:

          1. Natural Selection

          2. Mutation

          3. Genetic Drift

          4. Gene Flow

        • All mechanisms act concurrently on every living population

        Page 10: Natural Selection

        • Key evolutionary mechanism for adaptations

          • Adaptations: Heritable traits enhancing survival and reproductionThe Grants

            • Researchers: Peter and Rosemary Grant

              • Focused on finch populations on Daphne Island since 1973

            Page 13: Medium Ground Finches

            • Description of a finch species on Daphne Island

              • Characterized by stubby beaks

              • Primarily consume seeds

              • Grants tracked the population's changes over time

            Page 14: Beak Depth Variation

            • Functional adaptation:

              • Deeper beaks are advantageous for accessing large/hard seeds

              • Comparison between deeper and shallower beaks

            Page 15: The 1976 Drought

            • Significant drought event lasting 551 days

              • Resulted in shifts in seed availability

              • Prior data on finch population existence before and after drought analysis

The Grants

• Researchers: Peter and Rosemary Grant

  • Focused on finch populations on Daphne Island since 1973

Medium Ground Finches

• Description of a finch species on Daphne Island

  • Characterized by stubby beaks

  • Primarily consume seeds

  • Grants tracked the population's changes over time

Beak Depth Variation

• Functional adaptation:

  • Deeper beaks are advantageous for accessing large/hard seeds

  • Comparison between deeper and shallower beaks

The 1976 Drought

• Significant drought event lasting 551 days

  • Resulted in shifts in seed availability

  • Prior data on finch population existence before and after drought analysis

Population Changes (1976-1978)

• Population decline from 751 to 90 finches

• Average beak depth:

  • 1976: ~9.5 mm

  • 1978: ~10.2 mm

• Survival analysis favors deeper beaked finches during drought

Graph Interpretation Takeaways

• Heritability of beak depth: Offspring inherit traits from parents

• Importance of findings for evolutionary change

Established Conclusions

• Key points established:

  1. Variation existed in the population (beak depth)

  2. Beak depth is a heritable trait

  3. Deeper beaked finches were more likely to survive and reproduce

Darwin’s Postulates

1. Phenotypic variation exists within a population

2. Variation is genetically heritable

3. Differential reproduction/survival based on variation

• Natural selection occurs when these conditions are met

Evidence of Natural Selection

• The Grants document natural selection in action

  • Average beak size increased by 10% post-drought

Explanation of Enhanced Beak Depth

• Key factors described for beak depth increases in finches

  • Increased fitness among deeper beaked finches during drought led to their prevalence

Misconceptions of Natural Selection

• Natural selection is not based on needs or forward planning

  • Adaptations appear need-based but arise from existing traits

  • What is adaptive now may not remain so in the future

Challenges to Adaptation via Natural Selection

• Conditions that could hinder adaptation include:

  • Lack of variation in beak depth

  • Environmental determinism of beak depth

  • Complexity involving multiple genes

  • Absolute lack of necessary trait sizes

Understanding Fitness

• Definition of fitness in evolutionary terms (e.g., reproductive success)

• Fictional lizard comparison based on fitness metrics

  • Factors considered: body length, offspring survival, longevity, and adaptability.

LEC 2 - FEB 12

Fitness in Evolution

Overview

• Fitness: Term used by biologists to measure evolutionary success of an individual, often through reproductive success.

Measuring Fitness

• Fittest organisms successfully pass on their genes.

• Fitness is measured by the number of surviving offspring, not by strength or speed.

• Traits that enhance reproduction are adaptations.

  • Traits may include strength and speed if they aid survival/reproduction.

Seed Distribution and Natural Selection

• Question: Does natural selection act on finch beak depths if seed distribution remains stable?

  • Answer choices include: No, Yes (beaks deeper, narrower), or unsure.

Natural Selection and Trait Stability

• Natural selection often maintains stable traits within populations.

• Extremes of traits are less likely to survive and reproduce, leading to a heritable difference in fitness.

Types of Selection

Stabilizing Selection

• Selection where intermediate phenotypes yield higher reproductive fitness.

• Can shift distribution of traits and reduce variation.

Directional Selection

• Selection favours phenotypes at one end of a spectrum.

• Results in directional changes in traits within a population, e.g., 1976 drought affecting finch beaks.

Disruptive Selection

• Average traits decline in frequency while extreme traits are favoured.

• Common in specialists where adaptation is advantageous.

Challenge Questions

• Exploration of stability vs. change in evolution: If selection maintains trait stability, how is it considered an evolutionary process?

• 2003 drought impacts on finch populations post-introduction of large ground finches.

Phenotypic Frequencies and Natural Selection

• A fire reduces frog population, only 3 pink frogs survive. Questioning the frequency of 'pink' post-natural selection.

Evolution Mechanisms

• Evolution entails changes in heritable traits across generations influenced by:

  1. Natural Selection

  2. Genetic Drift

  3. Mutation

  4. Gene Flow

Genetic Drift

• Describes random changes in allele frequencies.

• Creates fluctuations in allele frequencies over time.

• More pronounced in small populations.

Punnett Square and Offspring Generation

• Two heterozygous iguanas (Rr) yield 8 offspring.

  • A Punnett square can illustrate potential genotypic outcomes.

  • True statements about offspring genotypes evaluated: frequencies of RR, Rr, and rr.

Chance in Survival and Reproduction

• Example involving medium ground finches, where survival is unpredictable despite strong selective pressures.

Genetic Drift Characteristics

• Discussion on which alleles are subject to random chance.

• Involvement across all heritable traits but less so on those under strong selection.

Changing Allele Frequencies

• Example of gene impacting female fertility.

• Explore the implications of genetic drift leading to fixation or loss of alleles.

Case Study: Island Snails

• Island population founded by 10 individuals isolated from the mainland.

• Statements regarding genetic drift and variation compared to the mainland are evaluated.

Summary of Genetic Drift

• Defined as changes in allele frequencies due to sampling error, affecting traits neared by natural selection.

• Occurs constantly but has a stronger impact on small populations.

• May cause detrimental alleles to increase in frequency.

Founders and Bottlenecks

Founder Effects

• Occur when a small group establishes a new population, leading to reduced genetic variation.

• Initial trait frequencies in the new population influenced by random chance.

Bottleneck Effects

• Result from rapid population decline that doesn’t depend on phenotypic traits.

• Events like floods or fires can create drastic shifts in trait frequencies.

Interaction of Natural Selection and Drift

• Both forces do not act in isolation.

• Suggested activity involves engaging with evolution simulations to explore these concepts.

Homework Assignment

• Calculate phenotypic, genotypic, and allelic frequencies for a specific frog population.

• Example population data provided for analysis.

IC 1: E

IC 2: BCD

IC 3: E

IC 4: BCE

IC 5: ACD

LEC 3 - FEB 24

• Natural selection causes alleles associated with higher fitness to increase in frequency.

• Genetic drift causes allele frequencies to change at random.

• Gene flow, in contrast, causes allele frequencies to change when individuals and their alleles move from one population to join another population.

Differences

• Random with respect to fitness, but in many cases alleles that arrive in recipient populations do not lead to high fitness in that environment.

  • Gene flow

• Random changes in DNA may make gene products work better, worse, or have no effect on fitness. But in populations that are well-adapted to their environment, random changes likely make gene products work worse in terms of fitness.

  • Mutation

• Increases fitness and leads to adaptation.

  • Natural selection

• Randomly impacts fitness — alleles increase or decrease in frequency just due to luck (sampling effects).

  • Genetic drift

Introduction to Evolution

• Evolution is the process that changes the proportion of heritable traits within populations from one generation to the next.

• Four key mechanisms of evolution:

  1. Natural Selection

  2. Genetic Drift

  3. Mutation

  4. Gene Flow

Page 5: Learning Objectives on Gene Flow and Mutation

• LO 12.2: Defend the statement "mutation is the ultimate source of genetic variation" and explain its randomness concerning an individual's fitness.

• LO 12.1: Define gene flow and describe its impact on allele frequencies in source and recipient populations.

Understanding Mutations

• Mutations: Changes in DNA caused by replication errors or exposure to mutagens.

• Two main types of mutations:

  • Genetic Mutations: Affect small numbers of nucleotides.

  • Chromosomal Mutations: Alter the number or structure of chromosomes.

• As an evolutionary mechanism, 'mutation' refers to an occurrence, while 'mutant' denotes a distinction from 'wild type.'

The Central Dogma and Phenotypic Significance

• The sequence of nucleotides in a gene influences:

  • mRNA sequence

  • Amino acid sequence in proteins

  • Structure and function of proteins

• The central dogma illustrates the significance of mutations on phenotypic traits.

True Statements About Mutations

• Evaluation of statements regarding mutations:

  • A: Not true; not all mutations alter the amino acid sequence.

  • B: True; mutations can create new alleles.

  • C: Not true; the most common outcome of mutations is often neutral.

  • D: True; mutations in gamete DNA introduce new variation.

  • E: False; mutations in somatic cells do not affect the broader population’s genetic pool.

Impact of Mutations on Fitness

• Mutations can be:

  • Beneficial: Enhance fitness.

  • Deleterious: Hinder fitness.

  • Neutral: No effect on phenotype (silent mutations).

• Impact varies based on circumstances.

Antibiotics and Mutation Rates

• The question of mutation rates that lead to antibiotic resistance:

  • A: 0 (no antibiotics): low mutation rate.

  • B: 1 (low concentration): moderate mutation rate.

  • C: 10 (medium concentration): high mutation rate.

  • D: 1000 (high concentration): could further solidify mutations.

  • E: None; antibiotics do not influence mutation likelihood.

Randomness of Mutations

• Mutations occur randomly concerning fitness;

• Environmental changes do not increase mutation likelihood.

• Example: Drought on Daphne Island—natural selection acted on pre-existing variations rather than creating new mutations.

Natural Selection's Role

• While mutations are random, natural selection enhances the frequency of beneficial mutations.

• In environments with antibiotics, antibiotic-resistant mutations are favored.

Frequency of Resistance Mutations

• New mutations for antibiotic resistance can only increase if under antibiotic selection pressures.

• Genetic drift can also impact the frequency of new genetic variants in populations.

Theoretical Scenario Without Mutations

• Consequences of no mutations:

  • A: Populations would become static and unable to evolve.

  • B: Species would be less likely to adapt to environmental changes.

  • C: Species would be more likely to go extinct.

  • D: Evolutionary impacts would become immediately apparent.

  • E: No new cancer cases would occur.

Mutations as a Source of Variation

• Mutations are fundamental for new genetic and phenotypic variability.

• Every allele originated from mutations; without them, no new genetic variation would arise.

Summary of Mutations

• Mutations are random mechanisms introducing genetic variation without a specific direction.

• Sufficient time and natural selection can harness these variations.

Case Study of Gene Flow

• A land bridge connects mainland and island frog populations.

• Yellow frogs migrate to the mainland, creating opportunities for new genetic combinations.

Impacts of Gene Flow

• Likely outcomes from the introduction of island frogs to the mainland:

  • A: New genotypes will emerge on the mainland.

  • B: Phenotypic variation may exceed previous mainland variations.

  • C: Allelic frequencies in both populations will converge.

  • D: The effect of gene flow on both populations may differ.

  • E: Average fitness of island frogs may change.

Understanding Gene Flow

• Gene Flow: The transfer of alleles between populations.

• A process that can increase genetic similarity among populations.

Hawk Predation of Yellow Frogs

• A hawk on the mainland preferentially preys on yellow frogs—impacting gene flow.

Effects of Predation on Gene Flow

• Consequences of hawk predation likely include:

  • A: No effect on fitness of island frog population due to gene flow.

  • B: Potential decrease in fitness of island frogs due to selective pressure.

  • C: Yellow frogs will not stop migrating due to predators.

  • D: Minimal effect on overall fitness of mainland frogs.

  • E: Likely decrease in fitness of the mainland frog population.

IC 1: B,D

IC 2: E

IC 3: False (b)

IC 4: C,E

IC 5: A,B,C

LEC 4 - FEB 26

Gene Flow and Population Dynamics

Definition of Gene Flow

• Gene flow is the exchanging of alleles between populations.

• Characteristics:

  • Can flow both ways between populations.

  • Reduces genetic diversity between populations.

  • Possible effects: negative, positive, neutral on population fitness.

  • Introduces new adaptive or non-adaptive variations.

Speciation and Gene Flow

Impact of Absence of Gene Flow

• Without gene flow, populations evolve independently.

• Leads to genetic and phenotypic divergence.

• Over time, this speciation can result in the formation of new species.

Evolution Mechanisms

Changes in Heritable Traits

• Definition of Evolution:

  • Proportional changes in heritable traits across generations.

• Four Mechanisms:

  1. Natural Selection

  2. Mutation

  3. Genetic Drift

  4. Gene Flow

• These mechanisms operate continuously within all populations.

Learning Objectives

Hardy-Weinberg Principle

• LO 13.1:

  • Explain why the Hardy-Weinberg principle acts as a null model for evolution.

  • Describe how natural selection, genetic drift, gene flow, mutation, and non-random mating can alter genotype frequencies compared to Hardy-Weinberg expectations.

• LO 13.2:

  • Identify expected genotype frequencies for a gene with multiple alleles under Hardy-Weinberg.

Understanding Evolution

• Evolution implies changes in heredity over time due to several mechanisms.

Key Questions

• Determining when a population is evolving requires observing deviations from expected results.

Null Hypotheses in Scientific Testing

• Essence of Null Hypothesis:

  • Testing hypotheses requires defining expected outcomes under conditions where effects are absent.

  • Actual observed data is compared against these predictions to assess validity.

Practical Testing of Hypotheses

• To assess an effect, define predictions for scenarios where that effect doesn't exist and evaluate actual data closely.

Concept of a 'Model'

Definition and Utility

• A model is a simplified representation of complex realities.

• Important Quote: "All models are wrong, but some are useful" - George Box.

  • Models can represent biological structures (e.g., cells) or ecological phenomena (e.g., geopolitics).

Evolutionary Modeling

Dynamic Nature of Evolution

• Evolution should be viewed not as static but as a continuously changing process reflected mathematically through allele and genotype frequency changes.

Developing a Null Model of Evolution

• Rules for simulating non-evolution:

  • A. Maintain a large population size (ideally infinite) to avoid sampling errors.

  • B. Prevent allele mutations.

  • C. No migration into or out of the population.

  • D. Ensure equal survival and reproduction chances for all genotypes.

  • E. Require random mating among individuals.

• Restrictions ensure no genetic drift, mutations, gene flow, or natural selection impact the model.

Hardy-Weinberg Equilibrium (HWE)

Definition and Assumptions

• HWE serves as a null model to assess if evolution occurs within populations.

• Five Assumptions of HWE:

  1. Infinite population size to avoid genetic drift.

  2. Absence of mutations.

  3. No migration.

  4. No natural selection forces.

  5. Random mating among individuals.

Genotype Frequencies and Observations

Determining Allele Frequencies

• Given known allele frequencies, we can calculate expected genotype frequencies under null conditions of evolution.

• Observed variations from predicted frequencies indicate evolutionary changes are occurring.

Example Problem - Allele Frequency Calculation

• Provided genotypes in a population are:

  • 4R4R: 436

  • 4R7R: 138

  • 7R7R: 41

• Calculate observed frequency of the 4R allele using the formula:

  • Formula: (2 × 4R4R + 4R7R) / (2 × total population).

Using Frequencies for Analysis

Genotypic Frequencies Calculation

• First step calculates expected 4R allele frequency.

Determining Frequency of Other Alleles

• Subtract 4R frequency from 1 to find frequency of the 7R allele.

Approaching Genotypic Frequencies in Evolution

• Once allele frequencies are known, derive expected genotypic frequencies as if no evolution is occurring.

Random Pairing and Frequency Calculations

Calculating Expected Pairing Frequencies

• Gametes pair randomly:

  • How to compute expected frequencies of pairing types:

    • A. Pairings with two 4R alleles: (p times p).

    • B. Pairings with one 4R and one 7R allele: (p times q).

    • C. Pairings of two 7R alleles: (q times q).

Simplifying Allelic Frequency Notation

Definitions for Variables

• Let:

  • p = frequency of 4R allele.

  • q = frequency of 7R allele.

Overall Expected Frequencies in Hardy-Weinberg Model

• To compute expected frequencies of offspring genotypes:

  • Use equations p^2 for homozygous 4R, 2pq for heterozygotes, and q^2 for homozygous 7R.

IC 1; E

IC 2: ALL ; A= no genetic drift, B= no mutation, C= no gene flow, D= no natural selection, E = no assortative mating

IC 3: B

IC 4: A

IC 5: A

IC 6: D

LEC 5 - MAR 3

Hardy-Weinberg Model Calculations

• Genetic combinations:

  • 4R x 4R: Offspring with 4R 4R

  • 4R x 7R: Offspring with 4R 7R

  • 7R x 7R: Offspring with 7R 7R

• Calculating the chances:

  • Chance of 4R with 4R = probability calculations

  • Chance of 4R and then 7R = pq

  • Chance of 7R and then 4R = qp

• Total probability calculation: pq + qp = 2pq

• Expected frequencies based on Hardy-Weinberg principle if no evolution occurs.

Allelic Frequencies and Genotypic Frequencies

• Definitions:

  • p: Allelic frequency of the 4R allele

  • q: Allelic frequency of the 7R allele

  • p2: Expected frequency of 4R 4R individuals under no evolution

  • 2pq: Expected frequency of 4R 7R individuals under no evolution

  • q2: Expected frequency of 7R 7R individuals under no evolution

Expected Frequency Calculation

• Question on expected frequency of 4R 4R individuals:

  • Options: A. 0.709, B. 0.674, C. 0.224, D. 0.067, E. "I got something totally different"

• Allele frequencies provided:

  • 4R: 0.821

  • 7R: 0.179

Expected Genotypic Frequencies under Hardy-Weinberg Equilibrium

• Frequencies under HWE:

  • 4R 4R: p2 = 0.71

  • 4R 7R: 2pq = 0.22

  • 7R 7R: q2 = 0.07

• Allele frequencies consistent with previous page.

Observed vs Expected Frequencies

• Observations show more homozygous 7R individuals than expected:

  • Observed Frequencies:

    • 4R4R: 0.71 (expected: 0.67)

    • 4R7R: 0.22 (expected: 0.29)

    • 7R7R: 0.07 (expected: 0.03)

• Possible interpretations:

  • A. 7R 7R genotype providing reproductive advantage.

  • B. Result of genetic drift.

  • C. Mutations for 7R must be occurring.

  • D. Ambiguity in data warrants additional statistical testing beyond the course.

Learning Objectives

• LO 14.1: Explain gene flow, inbreeding, and genetic drift's impact on endangered species in fragmented habitats.

Importance of Evolutionary Processes

• Understanding evolutionary mechanisms aids in:

  • Conservation efforts

  • Addressing health and disease issues

Effects of Habitat Fragmentation on Snakes

• Scenario: Highway divides snake population of 800 into:

  • 200 snakes (East)

  • 600 snakes (West)

• Analysis:

  • A. Reduced genetic variation in both subsets compared to the original population.

  • B. Increased inbreeding prevalence in new populations.

  • C. Genetic drift may make populations phenotypically similar.

  • D. Wildlife corridors facilitate gene flow.

  • E. Increased the genetic drift's impacts.

The Extinction Vortex

• Flowchart of extinction vortex:

  • Fragmentation/reduction reduces population size.

  • Leads to increased inbreeding.

  • Results in genetic drift and homozygosity.

  • Loss of alleles and genetic variability.

  • Increases frequency of deleterious phenotypes.

  • Decline in average fitness affects adaptability to environmental changes, worsening population size decline.

Recessive Deleterious Trait Example

• Alleles involved:

  • A: Dominant allele

  • a: Recessive deleterious allele

• Phenotypic outcomes:

  • AA: Common

  • Aa: Carrier of deleterious allele

  • aa: Expresses deleterious trait (rare).

Population Dynamics and Allele Frequencies

• In a large population with low 'a' frequency:

  • ¼ of Aa x Aa matings yield homozygous recessives (aa).

  • ½ of AA x Aa matings yield homozygous recessives (aa).

Impact of Highway on Population Genetics

• Visualization of genetic outcomes in isolated populations:

  • Increased likelihood of inbreeding.

  • Focus on changes in allele distribution and inherited traits.

Effects of Small Population on Inbreeding

• Small populations can increase:

  • Inbreeding rate.

  • Resulting in higher homozygous phenotypes and rates of deleterious traits.

Recap of the Extinction Vortex

• Review diagram emphasizing:

  • Population size reduction leads to increased inbreeding and effects of genetic drift.

  • Loss of genetic variability and its implications.

Adaptability to Changes

• Questions on reduced variation's impact on adaptability:

  • A. Reduced variation limits heritable traits for natural selection.

  • B. Natural selection acts only on existing variation.

  • C. Heterozygous genotypes are beneficial (not always true).

  • D. New mutations potentially increase fitness (not always sufficient).

PAntibiotics and Bacterial Resistance

• Beta-lactam antibiotics disrupt bacterial cell wall construction.

• Penicillin structure includes the beta-lactam ring facilitating bacterial death.

E. coli Resistant Populations

• E. coli may produce enzymes (beta-lactamases) that counteract antibiotic effects:

  • TEMwt (wild-type): unable to break down penicillin.

  • TEM* (mutation): 100,000x more effective against penicillin.

Genetic Differences in Resistance Alleles

• Five nucleotide differences between TEMwt and TEM*:

  • Sequence representation demonstrating mutations in the genes.

Page 21: Continued Discussion on Genetic Divergence

• Detailed sequence assemblies showing five point mutations between TEMwt and TEM*.

Mechanisms of Evolution for Resistance

• True/False question regarding mutation accumulations:

  • A. True in the presence of penicillin.

  • B. True regardless of conditions.

  • C. False, unlikely to happen all at once.

Evolutionary Steps for TEM* Allele

• Collaborative discussion on realistic pathways to evolve from TEMwt to TEM*.

Intermediate Alleles and Antibiotic Resistance

• Exploring the potential advantages of intermediate mutations leading to antibiotic resistance.

Mutation Pathways Analysis

• Consideration of intermediate alleles for achieving full resistance:

  • Options on how mutations interact and lead to evolutionary outcomes.

Gradual Improvements in Resistance

• Explanation of how individual mutations may confer slight advantages:

  • Details of sequences from TEMwt to TEM* indicating gradual increases in resistance.

Testing Mutation Effects

• Research conclusion on mutation orders influencing resistance:

  • 120 ways for mutation combinations, testing results of varying success.

Historical Context of Mutation Studies

• Review of Weinreich et al. (2006)

  • Findings on the mutation orders facilitating TEM* allele evolution via natural selection.

Fast-Tracking Complex Adaptations

• Importance of intermediate phenotypes in accelerating adaptation through mutation and natural selection.

Purpose of hardy: when evolution DOES NOT occur, we can determine the frequency of alleles.

IC 1: B

IC 2: D

IC 3: A,B,D

IC 4: B

IC 5: C

IC 6: A

LEC 6 - MAR 5

• Speciation

  • is the process that creates new types, or species, of organisms. It is a splitting event, where one species breaks into two or more separate species. The initial group is sometimes called the ancestral species while the subsequent groups are referred to as descendant or daughter species.

Speciation is a two-step process:

1. Genetic Isolation

   When gene flow between two populations of the same species is interrupted, genetic isolation occurs. This prevents allele mixing, leading to independent evolution of the populations.

2. Genetic divergence
   
   Once isolated, populations can diverge due to mutation, natural selection, and genetic drift. Variations in environments may cause different alleles to be favoured, leading to increasingly distinct genetic and phenotypic traits. Over time, each population may evolve into a separate species as mutations in one population do not transfer to the other.

Common House Mosquito

• Culex pipiens: Found in temperate and tropical regions, hibernates in winter, tolerates cold.

London Underground Mosquito

• Culex molestus:

  • Found in the London Underground system, stable temperature and humidity, typically breeds year-round, does not tolerate cold.

  • Bites various hosts including rats, mice, and humans.

Distinction Between Species

• Two populations of mosquitoes likely descended from one ancestral population:

  • Ancestral Population

  • London Underground Population

  • Aboveground Population

• Definition of a population: Regular mating individuals from the same geographic area.

Requirements for New Species

• What is necessary for populations to become separate species?

  • A) Gene flow

  • B) Genetic isolation

  • C) Genetic divergence

  • D) Natural selection

  • E) All of the above

Genetic Isolation and Speciation

• Speciation: Involves genetic isolation and divergence creating new species, results from lack of gene flow.

• Factors causing genetic isolation can include:

  • Geographic barriers

  • Resource availability

  • Temporal shifts (breeding seasons)

  • Mating behaviors

Types of Speciation

Allopatric Speciation

• Occurs when gene flow is interrupted by a geographic barrier, isolating populations.

Sympatric Speciation

• Occurs in the same geographic area but is split by reproductive barriers. Example: Variations that create differences in breeding times leading to assortative mating.

Example of Genetic Isolation

• A lineage of plants, mutated to attract hummingbirds instead of bees, represents genetic isolation without a geographic barrier.

Driving Forces of Genetic Divergence

• Once gene flow is interrupted, genetic divergence can be driven by:

  • Mutation

  • Genetic drift

  • Natural selection

Exploring Genetic Isolation

• Genetic isolation may occur instantly, gradually over time, or through other dynamics.

Species Definition

• A species is defined as an independent evolutionary unit, characterized by:

  • Genetic isolation from other populations.

  • Adaptations through natural selection, genetic drift, and mutation.

Biological Species Concept

• Defines species as groups of interbreeding natural populations that are reproductively isolated from other groups.

Fertility of Offspring in Species

• Examples of reproductive barriers:

  • Offspring may be sterile or not develop affected species.

Complexity of Species Concepts

• Challenges arise regarding:

  • Asexual species

  • Hybrid organisms

  • Fossils and connected extremes in species.

Evidence for Different Species

• Suggestions that two populations are different species include:

  • Offspring from interbreeding are sterile.

  • The populations do not interbreed when in contact.

  • Offspring do not mature.

  • Interbreeding attempts fail.

  • Offspring can interbreed with either population.

Renaming of the London Underground Mosquito

• In 2012, it was reclassified as a special form of the Common House Mosquito: Culex pipiens f. molestus.

Genetic Evidence for Divergence

• Studies show that the London Underground Mosquito is genetically distinct from the Common House Mosquito, with infertile crossbred eggs indicating reproductive isolation.

Current Understanding

• There is ongoing debate regarding whether the London Underground Mosquito and Common House Mosquito comprise one or two species, with historical origins tracing back thousands of years.

IC 1: B,C

IC 2: E

IC 3: A,C,D