Study/Discussion Q&A

CHAPTER 19

You should now be able to

• Explain how Darwin’s voyage on the Beagle influenced his thinking.

  • They realized organismal traits fit environments and fossils remains resembled living species in the same region. Living species looked like nearby species

• Explain why the concept of evolution is regarded as a theory with great significance.

• Explain how fossils form and why the fossil record is incomplete.

• Explain how homologies, the fossil record, and molecular biology support evolution.

  • Fossil Record → Shows life is very old and has changed over time through evolution

  • Homology → Similarity due to common ancestry

• Describe Darwin’s observations and inferences in developing the concept of natural selection.

• Explain how the work of Thomas Malthus and the process of artificial selection influenced Darwin’s development of the idea of natural selection.

• Explain why individuals cannot evolve and why evolution does not lead to perfectly adapted organisms

  • Individuals cannot evolve because they will always be AA , Aa, aa

• Describe two examples of natural selection known to occur in nature

• Explain how antibiotic resistance evolves.

• Explain why natural selection cannot produce perfect organisms.

• Describe the difference between homologous and analogous traits

Learning Objectives

• counter common misconceptions about evolution (throughout this unit)

  • Evolution is ‘just a theory’, natural selection, entirely random, provides species with adaptations they ‘need’ or ‘want’, the result of individuals adapting to their environment, a march of progress

  • Organisms are perfectly adapted to their environment

  • Some forms of life are ‘more evolved’ than others

• Understand how the concepts of evolution and natural selection developed

  • Concept of evolution

    • The earth is older than previously realized

    • Dissimilar fossils of extinct animals

• Describe the observations and inferences of natural selection

  • Traits vary and these variations are heritable

  • More offspring are produced than can survive; there is a competition for resources

• Describe examples of evidence that support the theory of evolution

  • The earth is older than previously realized

  • Dissimilar fossils of extinct animals

• Know the difference between analogy and homology and give
  examples of each

  • Homologous structure → traits that are similar in structure (due to common ancestry) despite being used in different ways

    • Ex) Arm

  • Analogous traits → similar traits but not because of common ancestry

    • Ex) shark, penguin, and dolphin all have similar fin structures

CHAPTER 20

You should now be able to..

1. Explain how homologies, the fossil record, and molecular biology support evolution.

2. Explain how evolutionary trees are constructed and used to represent ancestral relationships.

   • As lineages evolve and modifications are inherited from common ancestors, their evolutionary paths diverge with can produce a branching pattern of evolutionary relationships

     • evolution creates branching patterns

3. Be able to read and understand phylogenetic trees

   • Monophyletic: An ancestor and all its descendants

   • Paraphyletic: An ancestor and some of its descendants

   • Polyphyletic: Distantly related species, no ancestors

4. Understand how phylogenetic trees are built from morphological and genetic data

5. Be able to correctly use phylogenetic terminology

6. Be able to use a molecular clock to estimate divergence times between two lineages

   • Differences in gene sequences between groups can be used to estimate divergence time

     • Ex) A gene mutates at a rate of 1 bp/100,000 years of 6bp different diverange occurred 600,000 years ago

7. Understand how horizontal gene transfer complicates prokaryotic phylogenies

Learning Objectives

• Be able to read and understand phylogenetic trees

• Understand that phylogenetic trees are built from homologous morphological and genetic data

• Correctly use phylogenetic terminology (nodes, branches, MRCA)

• Use a molecular clock to estimate divergence times between two lineages

CHAPTER 21

Extensions to HWE equations

• Triploid organisms

  • (p + q)3 = 1

  • p3 + 3p2q + 3pq2 + q3 = 1

• One locus three alleles

  • (p + q + r)2 = 1

  • p2 + q2 + r2 + 2pq + 2pr + 2qr = 1

• One locus four alleles

  • (p + q + r + s) 2 = 1

  • p2 + 2pq + q2 + 2qr + r2 + 2pr + s2 + 2ps + 2qs + 2rs = 1

Important Hardy-Weinberg Principle equations

• Population Allele frequency

  • p = f(A) = f(AA) + f(Aa)*0.5

  • q = f(a) = f(aa) + f(Aa)*0.5

• Sum of population allele frequencies should add up to 1 (gene pool)

  • p + q = 1

  • q = 1 - p

• Hardy-Weinberg equilibrium (expected genotype frequencies in a population with no evolution)

  • (p + q)2 = 1

  • p2 + 2pq + q2 = 1

Think-pair-share

Fill in the blank summary

• If there is random mating within a population and no evolutionary forces act on it, allele frequencies will not change across generations (maintain genetic diversity)

• HW-Principle is used to test whether a population is evolving

• If observed genotype frequencies match what is predicted by HW-principle, the population is in Hardy-Weinberg Equilibrium and is not evolving

• The assumptions of a population in HWE are no genetic drift, no migration, no mutation, no natural selection, and complete random mating

• The Hardy-Weinberg principle is used to estimate expected genotype frequencies (based on random mating and no evolution), given observed allele frequencies

You Should Now Be Able to...

1. Explain why individuals cannot evolve and why evolution does not lead to perfectly adapted organisms.

   • Individuals cannot evolve because they don’t have any allele frequencies or genetic variation like a population does

   • population = gene pool.

2. Describe two examples of natural selection known to occur in nature.

3. Explain how mutation and sexual reproduction produce genetic variation.

   • Genetic variation refers to the diversity of alleles in a population

   • Random genetic drift reduces genetic variation through loss of alleles

4. Describe the five conditions required for the Hardy-Weinberg equilibrium.

   • No mutations

   • Random mating

   • No natural selection

   • Extremely large population size, so there’s no genetic drift

   • No gene flow = no migration

5. Explain why the Hardy-Weinberg equilibrium is significant to understanding the evolution of natural populations and to public health science.

6. Define genetic drift and gene flow. Explain how the bottleneck effect and the founder effect influence microevolution.

   • Gene flow = Migration

     • Movement of individuals among populations

   • Bottleneck → Rapid environmental change causes extreme reduction in size of a population

   • Founder Effect → when drift is increased. A small number of individuals start a new population. Explains the relatively high frequency of inherited diseases in some populations

7. Distinguish between stabilizing selection, directional selection, and disruptive selection. Describe an example of each.

   • Stabilizing Selection → Individuals with intermediate phenotype favored; extreme phenotypes elected against

   • Directional Selection → Individuals of one extreme phenotype favored

     • Humans use directional selection to create turkeys and chickens with large breast muscles

   • Disruptive Selection → Both extreme phenotypes favored; intermediate phenotypes selected against

8. Define and compare intrasexual selection and intersexual selection.

   • INTRAsexual selection → competition within the same sex(males); Sperm competition

   • INTERsexual selection → one sex (females) is ‘choosy’, also called mate choice

9. Explain how antibiotic resistance evolves.

10. Explain how genetic variation is maintained in populations.

11. Explain why natural selection cannot produce perfection.

    • The Hardy-Weinberg Principle demonstrates that dominant alleles do not inevitably become more common in a population and therefore populations are able maintain more than one allele in the absence of evolutionary (HW-assumptions) processes.

• If the observed genotype frequencies equal the frequencies predicted by the Hardy-Weinberg principle, is the population in HW equilibrium?

  • Yes

• What does this suggest about evolution in the population?

  • Suggests no evolution and random mating is occurring

Think-pair-share

Wrap-up

• What are the assumptions of the Hardy-Weinberg Principle?

  • Infinite population size (No genetic drift)

  • No Natural selection

  • No Mutation

  • No Gene flow (immigration/emigration)

  • Complete random mating

• If a population mates randomly and no evolution occurs, will the dominant allele become more common in a population? Why or why not?

  • No, Allele frequencies (p and q) for a gene remain constant across generations as long as assumptions are met

Learning Objectives

• Define evolution, population, and identify that genetic variation is necessary for evolution

  • Evolution → changes in allele frequencies within a population over generations = microevolution

  • Population → A group of individuals within a species that live in same area and are capable of producing fertile offspring

  • Genetic variation refers to the diversity in heritable traits is necessary for evolution by natural selection

• List the assumptions of the Hardy-Weinberg Principle

  • No natural selection

  • No mutations

  • No Migration

  • No genetic drift(infinite population size)

  • Complete random mating

• Calculate allele and genotype frequencies (observed and expected under HWE) in populations

• Use this information to determine if a population is evolving

• Recognize that dominance alone does not change allele frequencies at a locus

• Describe the four ways populations evolve and how different types of natural selection affect allele frequencies in populations