The Evolution of Populations
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
16-1: Genes and Variation
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.
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.
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