Chapter 16
The Evolution of Populations

In this chapter, students will read about how genetic diversity and changes in the genetic makeup of populations contribute to evolution. Students will also read about types of and mechanisms of natural selection and the process of speciation. The links below lead to additional resources to help you with this chapter. These include Hot Links to Web sites related to the topics in this chapter, the Take It to the Net activities referred to in your textbook, a Self-Test you can use to test your knowledge of this chapter, and Teaching Links that instructors may find useful for their students.

What are Web Codes?

Web Codes for Chapter 16: Antibiotics in Animal Feed (Issues) SciLinks: Population Genetics SciLinks: Speciation Self-Test

Section 16-1: Genes and Variation
Biologists have discovered that there are two main sources of genetic variation: mutations and the genetic shuffling that results from sexual reproduction.
The number of phenotypes produced for a given trait depends on how many genes control the trait.

Section 16-2: Evolution as Genetic Change
Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution.
Natural selection can affect the distributions of phenotypes in any of three ways: directional selection, stabilizing selection, or disruptive selection.
In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population.
Five conditions are required to maintain genetic equilibrium from generation to generation: there must be random mating; the population must be very large; and there can be no movement into or out of the population, no mutations, and no natural selection.

Section 16-3: The Process of Speciation
As new species evolve, populations become reproductively isolated from each other.
Speciation in the Galápagos finches occurred by founding of a new population, geographic isolation, changes in the new population's gene pool, reproductive isolation, and ecological competition.