chapter 14

population

a group of organisms of the same species populating a given area

stabilizing selection

a type of natural selection in which organisms near the middle of the phenotypic range of variation are favored by the environment.

diversifying selection

a type of natural selection in which organisms with phenotypes at both extremes of the phenotypic range are favored by the environment

directional selection

a type of natural selection in which organisms with phenotypes at one end of a spectrum are favored by the environment

Describe the relationship between natural selection, adaptation, and evolution. Be able to apply to new contexts (see test your knowledge question 21 and examples in the powerpoint)

- Natural selection: the differential survival and reproduction of individuals within a population in response to environmental pressure - advantageous traits become more common and population becomes "better suited", or adapted, to environment - over time, population evolves

Outline the specific steps of natural selection.

1. A population has genetic variations 2. some variations are favorable in a particular environment 3. more offspring are produced than survive 4. those offspring that do survive have the favorable trat(s) for that environment 5. a population changes genetically over time to become better adapted to its environment

fitness

Ability of an organism to survive and reproduce in its environment

Why do bacteria populations evolve so quickly so we can observe it happening?

Bacteria reproduce asexually by a process called binary fission. Asexually reproducing bacterial populations become genetically diverse by accumulating mutations and by picking up genes from organisms of the same or different species. Gene diversity can happen by two ways: 1. mutation: during DNA replication introduces new alleles that were not present in the population before 2. Gene transfer: between bacterial species introduces new alleles

Explain the relationship between phenotype, environment, and fitness.

Fitness simply means reproductive success and reflects how well an organism is adapted to its particular environment. Ex: the brown beetles had higher "fitness" in the drought environment.

Recognize how mutations create new alleles some of which are resistant to an antibiotic (no specific question on bacteria, gene transfer, etc). Without mutation, the process of natural selection would not work.

bacteria can become resistant to drugs either by mutations in their own genes or by picking up "resistance" genes from other drug-resistant bacteria. The altered or acquired genes either code for proteins that can disable antibiotics, or they code for proteins with altered shapes to which antibiotics can no longer bind.

evolution

change in allele frequencies in a population over time

environmental selective pressure

something in the environment that causes a specific trait to be more successful (better able to survive and reproduce)

adaptation

the process by which the characteristics of a species change over many generations in response to the environment

Be able to explain that while mutation is a random process, natural selection is not random.....it drives the production of adaptations in populations by choosing the members who best "fit" the environmental conditions.

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Explain how adaptations that develop via natural selection can lead to speciation (this part comes later in other chapters but be able relate back to Darwin's idea of natural selection that can eventually lead to descent with modification (new species forming as time goes by).

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Know that mutation is the random part of the process of natural selection. Mutations provide nature something to "select" to drive the production of adaptations.

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