Genetic Variation
Within Populations
Genetic Variation is stored in a population’s
Gene Pool-- The combined alleles of all of the
individuals in a population.
Genetic Variation comes from 2 main sources:
1. Mutation: random changes in DNA
2. Recombination: Sexual reproduction.
Natural Selection Acts on Distribution of Traits.
Environmental conditions can change and certain phenotypes may become an advantage.
3 Types of Natural Selection are:
1. Directional Selection: Favors phenotypes at one extreme of a traits range.
2. Stabilizing Selection: The intermediate phenotypes are favored and become the
most common in the population.
3. Disruptive Selection: Both extreme phenotypes are favored.
Sexual Selection: Occurs when certain traits
increase mating success.
These traits are not always adaptive for the
survival of the individual.
Artificial Selection: Humans make use of the genetic
variation of plants and animals by acting as the selective
agent. Humans determine which traits are favorable or not.
Other Mechanisms of Evolution
Gene Flow: The movement of alleles from one population to
another.
Founder Effect: Is genetic drift that occurs after a small
number of individuals colonize a new area. The gene
pools of these populations are often different from the
larger populations.
Evolution through Natural Selection is Not Random
Mutation and genetic drift cannot be predicted, they are
random events. These random events are sources of
genetic diversity.
However, natural selection, which acts on diversity, is not
random. Individuals with traits that are better adapted to
their environment have a better chance of surviving and
reproducing that do individuals without these traits.
Convergent Evolution:
Evolution toward similar
characteristics in unrelated
species.
Divergent Evolution: When closely related species
evolve in different directions. Different adaptations
for different environments.
Coevolution: the process in which two or more
species evolve in response to each other.
The RED QUEEN THEORY
Extinction: The elimination of a species from Earth.
Background Extinction: Occur continuously but at a very
low rate.
Mass Extinction: Much more rare. Operate at the global
level. The fossil record confirms there have been 5 mass
extinctions in the last 600 million years.