Natural Selection

*Enduring Understanding 1.A: Change in the genetic makeup of a population over time is evolution.

- Essential Knowledge 1.A.1: Natural selection is a major mechanism of evolution.

• a. According to Darwin's theory of natural selection, competition for limited resources results in different survival. Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing traits to subsequent generations.
• b. Evolutionary fitness is measured by reproductive success.
• c. Genetic variation and mutation play roles in natural selection. A diverse gene pool is important for the survival of a species in a changing environment.
• d. Environments can be more or less stable or fluctuation, and this affects evolutionary rate and direction; different genetic variations can be selected in each generation.
• e. An adaptation is a genetic variation that is favored by selection and is manifested as a trait that provides an advantage to an organism in a particular environment.
• f. In addition to natural selection, chance and random events can influence the evolutionary process, especially for small populations.
• g. Conditions for a population or an allele to be in Hardy-Weignberg equilibrium are: (1) a large population size, (2) absence of migration, (3) no net mutations, (4) random mating and (5) absence of selection. These conditions are seldom met.
• h. Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population.
  • Learning Objectives:
    • LO 1.1: The student is able to convert a data set from a table of numbers that reflect a change in the genetic makeup of a population over time and to apply mathematical methods and conceptual understandings to investigate the cause(s) and effect(s) of this change
    • LO 1.2: The student is able to evaluate evidence provided by the data to qualitatively and/ or quantitatively investigate the role of natural selection in evolution
    • LO 1.3: The student is able to apply mathematical methods to data from a real or simulated population to predict what will happen to the population in the future.

-Essential knowledge 1.A.2: Natural selection acts on phenotypic variations in populations.

• a. Environments change and act as selective mechanism on populations.
• b. Phenotypic variations are directed by the environment but occur through random changes in the DNA and through new gene combinations.
• c. Some phenotypic variations significantly increase or decrease fitness of the organism and the population.
• d. Humans impact variation in other species.
  • Learning Objectives:
    • LO 1.4: The student is able to evaluate data-based evidence that describes the evolutionary changes in the genetic makeup of a population over time.
    • LO 1.5: The student is able to connect evolutionary changes in a population over time to a change in the environment.

Essential Knowledge 1.A.3: Evolutionary change is also driven by random processes.

• a. Genetic drift is a nonselective process occuring in small populations.
• b. Reduction of genetic variation within a given population can increase the differences between populations of the same species.
  • Learning Objectives:
    • LO 1.6: The student is able to use data from mathematical models based on the Hardy-Weignberg equilibrium to analyze genetic drift and effects of selection in the evolution of specific populations.
    • LO 1.7: The student is able to justify the selection of data from mathematical models based on the Hardy-Weignberg equilibrium to analyze genetic drift and the effects of selection in the evolution of specific populations.
    • LO 1.8: The student is able to make predictions about the effects of genetic drift, migration and the artificial selection on the genetic makeup of a population.