D4.1  Natural Selection

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.​

• What processes can cause changes in allele frequencies within a population?
• What is the role of reproduction in the process of natural selection?

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How do intraspecific interactions differ from interspecific interactions? 
• What mechanisms minimize competition?

D4.1.1— Natural selection as the mechanism driving evolutionary change.

• Define natural selection.
• Outline the observations and inferences that lead to the development of the theory of evolution by natural selection. 
• Outline the theory of evolution by natural selection as an example of inductive reasoning.
• Outline the theory of evolution by natural selection as an example of the correspondence, coherence and pragmatic theories of truth.
• State that natural selection has operated continuously over billions of years, resulting in the biodiversity of life.​

D4.1.2— Roles of mutation and sexual reproduction in generating the variation on which natural selection acts.

• Explain why natural selection can only function if there is variation in a species.
• Outline sources of genetic variation (mutation, meiosis and sexual reproduction). 
• Compare variation that results from mutation to that generated from sexual reproduction.

D4.1.3-- Overproduction of offspring and competition for resources as factors that promote natural selection.

• State that species have the ability to produce more offspring than the environment can support.
• Use an example to illustrate the potential for overproduction of offspring in a population.
• State two evolutionary benefits of overproduction of offspring.
• Describe competition for resources as a consequence of overproduction of offspring.
• Define carrying capacity
• List examples of resources that may limit population size.
• Compare direct and indirect competition.

D4.1.4--  Abiotic factors as selection pressures.

• Define selective pressure and density-independent.
• State example biotic and abiotic selective pressures.
• Outline how a selective pressure acts on the variation in a population.​

D4.1.5— Differences between individuals in adaptation, survival and reproduction as the basis for natural selection.  

• Define adaptation and fitness.
• Explain the effect of the selective pressure on the more and less adapted individuals in a population.
• Explain adaptation as a consequence of natural selection. ​

D4.1.6- Requirement that traits are heritable for evolutionary change to occur.

• Distinguish between heritable and acquired characteristics. 
• Explain why only heritable characteristics can be acted upon by natural selection.

 ​​​​D4.1.7- Sexual selection as a selection pressure in animal species.

• Outline the two major mechanisms of sexual selection in evolution of courtship behavior and anatomical features. 
• Describe examples of sexual selection, including for color, size, and courtship behaviors.

D4.1.8- Modelling of sexual and natural selection based on experimental control of selection pressures.  

• Outline the selective pressures for and against coloration in guppies.
• Summarize John Endler’s experiments with guppies which demonstrate selection for and against coloration in different habitats.
• Explain what models are and their purposes in science.
  

AHL ​​​​​​​D4.1.9- Concept of the gene pool.

• Define gene pool, gene, allele and gene flow.
• Describe how it is possible for multiple gene pools to exist in a single species.

AHL ​​​​​​​D4.1.10- Allele frequencies of geographically isolated populations.

• Define allele frequency.
• Calculate allele frequency from gene pool data. 
• Outline reasons when allele frequencies may be different in geographically isolated populations of the same species.
  
• Use a database to search for allele frequency of a human gene.​

AHL ​​​​​​​D4.1.11- Changes in allele frequency in the gene pool as a consequence of natural selection between individuals according to differences in their heritable traits.

• Outline “neo-Darwinism” as the integration of genetic inheritance and the mechanism of natural selection.
  
• State that change in the allele frequencies of a gene is evidence of evolution.
• List processes that can change allele frequency in a population.
  
• Explain how natural selection can lead to change in allele frequency in a gene pool. ​

AHL ​​​​​​​D4.1.12- Differences between directional, disruptive and stabilizing selection.

• Outline the change in allele frequencies associated with stabilizing, disruptive and directional selection.
• Use graphs to illustrate or identify stabilizing, disruptive and directional selection.
• Outline an example of stabilizing, disruptive and directional selection.​

AHL ​​​​​​D4.1.13- Hardy–Weinberg equation and calculations of allele or genotype frequencies.

• State the Hardy-Weinberg equations.
• Given data, calculate allele frequencies of a gene in a gene pool.
• Given data, calculate genotype frequencies of a gene in a gene pool.​

AHL ​​​​​​D4.1.14- Hardy–Weinberg conditions that must be maintained for a population to be in genetic equilibrium.

• List the conditions under which populations maintain Hardy-Weinberg equilibrium.
• Explain how comparison of allele frequencies between two isolated populations of the same species can serve as evidence that divergence is (or is not) occurring.
• Explain how comparison of allele frequencies between one population at two points in time can serve as evidence that evolution is (or is not) occurring.​

AHL ​​​​​​D4.1.15- Artificial selection by deliberate choice of traits. 

• Define artificial selection.
• Outline the mechanism of artificial selection in evolution of crop plants and domestic animals.
• Describe an example of artificial selection of a crop plant or domestic animal.​