Download Natural Selection - David Brotherton CCCMC

Biology
Class Notes
Lesson 28 Natural Selection
Objective: 3.4.2, 3.4.3
Species: A group of organisms that can interbreed to produce fertile
offspring.
• Organisms thrive in environments where they are best suited.
• Species develop/evolve characteristics to help them survive in their
environments.
Speciation: The evolutionary process that produces new species.
Gene Pool: All the genes or genetic variation within a population.
Variation: Differences among members of a species.
• If variation gives an organism an advantage in its environment, it will
be more likely to survive and reproduce.
Inheritable Characteristics: Variation in an organism that is inheritable (i.e.
passed to offspring).
Methods of Speciation
Geographic Isolation
• The physical separation of members of a population that results in the
inability to mate.
• Can be caused by bodies of water, mountains, valleys, deserts, etc.
• Natural selection on each side of the barrier causes the populations to
become genetically different.
Reproductive Isolation
• Barriers to successful breeding between population groups in the same
area.
• Can be caused by: incompatible behavior (mating calls that aren’t
recognized), differences in mating times, or physical differences that
cause individuals to choose specific, nonrandom mates.
• Nonrandom mating causes genetic differences.
Parapatric Isolation
• Can affect two neighboring populations living in different
environments next to one another.
Ex: Dry vs. wet, cool vs. hot, high altitude vs. lower altitude, etc.
• Natural selection favors different adaptations in each environment and
the populations become genetically different.
Behavioral Isolation
• Results from differences in behaviors, such as choosing to migrate at
different times that prevent mating.
• Selection of nonrandom mates results in genetic variation
Natural Selection: The nonrandom process by which biologic traits become
more or less common in a population as a function of differential
reproduction (i.e. organisms best suited for their environment, as a result
of favorable characteristics, will survive and reproduce).
• First proposed by Charles Darwin
1. Most organisms produce more offspring than can survive.
2. This results in competition for resources.
3. Some offspring will have variations that make them better at
competition and better able to survive.
4. Successful organisms reproduce and pass these successful traits to
their offspring.
5. Over time, these successful traits are found in more and more
offspring.
Adaptation
• A trait that improves an organism’s chance for survival and
reproduction.
• Adaptations lead to favorable traits that lead to evolution…
Types of Natural Selection
Stabilizing Selection
• Individuals with the average form of the trait have the highest fitness
Directional Selection
• Individuals with one extreme form of a trait that results in greater
fitness over individuals with an average form of a trait.
Disruptive Selection
• Individuals with either extreme variation of a trait have greater fitness
than individuals with the average form of the trait
Sexual Selection
• Females choose the males they mate with based on certain traits (e.g.
brightly colored feathers, strength, intelligence, speed).
• The traits communicate a male’s fitness to the females.
Antibiotic Resistance
 Natural antibiotics and bacteria have always evolved.
 A form of drug resistance in which sub-populations of resistant bacteria
flourish while non-resistant sub-populations are eliminated.
 Leads to new infections that are not treatable with conventional
antibiotics.
 Bacteria that develop resistance to first and second line antibiotics are
called Multidrug Resistant or MDR (a.k.a Superbugs).
Should you take antibiotics when you are not sure about whether an illness is
caused by a bacterial infection?
Problem Set: Darwin and Types of Selection
Problem Set: Types of Natural Selection
Key Words:
Evolution
Species
Natural selection
Adaptation
Gene pool
Fitness
Speciation
Resistance
Immunity
Antibiotic