Download File

Chapter 11 Notes/ Continuation of Unit 10
Genetic Variation
Why is it beneficial: It is beneficial because it allows for variation in phenotypes of individuals
in a population. This allows for individuals to survive when their habitat changes. P. 308
How is it stored in a population: It is stored in a populations gene pool. A gene pool is ALL of
the alleles in a population. Variety arises when different organisms reproduce with each other.
How is it measured: It is measured by allele frequency, this is a measure of how common a
certain allele is in a population. To measure this count the number of times an allele occurs in a
gene pool and then divide it by the total number of alleles for that gene.
Variation comes from two main sources: Mutations and Recombination
Mutation: Random change in the DNA of a gene. Can be passed along if in a reproductive cell.
Increases variation due to new genes and many individuals in a population. Happens often.
Recombination: New allele combinations in an offspring. Mostly occurs during meiosis.
Hybridization is being researched as a possible 3rd way of variation due to how common it is
with in plant and mammals
11.2 Natural Selection in Populations
Normal distribution: Frequency is highest near mean value and decreases toward each extreme
end of range. In the graph you will see a bell shaped curve.
This is seen when all phenotypes provide an equal chance of survival. Phenotypes close to the
middle are generally most common. This can shift based on the environment. Nature favors the
phenotypes that are in the middle of the curve and allow for the most survival and most
reproduction.
Microevolution: Observable change in the allele frequency of a population over time. Occurs on
a small scale “Micro = small”. Natural selection can lead to microevolution. Natural selection
can change the distribution in 1 of 3 ways: disruptive, stabilizing, and directional
Disruptive selection: Occurs when both extremes are favored. Ex: feather color of the male lazuli
bunting
Stabilizing Selection: Intermediate phenotype becomes more common in the population.
Increases organisms with an intermediate phenotype. Decreases the genetic diversity of
individuals in the population.
Directional Selection: Favors one extreme more than another and shifts to that extreme, causes a
shift in the phenotypic distribution. This causes the extreme phenotype to become more
common.
11.5 Speciation Through Isolation 324-326
Reproductive Isolation: Occurs when members of different populations can no longer
successfully mate. Can occur because of something physical or because the offspring can’t
survive and reproduce. This is the final step in a species splitting into 2 different species.
Speciation: This is the rise of two or more species from one existing species. Be able to
explain the fruit fly experiment on page 324 and 325 to explain this further.
Reproductive Isolation can be caused in 3 ways: Behavioral Barriers, Geographic Barriers,
and Temporal Barriers
Behavioral Barriers- Isolation based off of changes in mating behaviors of different species.
Very common in fireflies
Geographic Barriers- Most commonly studied, physical barriers that divide the group into
2 or more different sections. Includes divides such as rivers, mountains, lakes etc. This
types of organisms may look physically the same but genetically are very different.
Temporal Barriers- When timing prevents reproduction. Different populations may mate
at different times if there is an increase in competition. By this change in reproduction
speciation may occur. Ex. Pine trees on the Monterey peninsula in California
11.6 PATTERNS IN EVOLUTION
Convergent Evolution- Evolution towards similar characteristics in unrelated species. Ex:
Analogous Structures
Specific Examples: Wings on birds and insects, Tail fin of sharks and dolphins
Divergent Evolution- Related species evolve in different directions and become increasingly
more different
Specific Example: Red Fox and Kit Fox
Coevolution: Process in which two or more species evolve in response to changes in each other.
Ex: Acacia plant and ants that live in the acacia
Evolutionary arms race: Species respond to pressure from the other through better adaptations
over many generations. Ex: Pesticides, Crabs and Murex snails
Extinction: Elimination of species from Earth. Usually occurs when a species as a whole is
unable to adapt to changes in environment or habitat.
2 Categories: Background and Mass
Background: Occur continually but at a very very slow rate. Occur at same rate as speciation.
Affect only a few species in a small area. They are usually caused by a change in the
environment of the organism.
Mass: Very Rare!!! Very intense and cause a large scale change. Occur on a global level and not
just isolated. Can wipe out an entire family or order from a taxonomic level. Happen very fast
with something like an ice age or asteroid. Fossil record shows that this has occurred at least 5
times in the last 600 million years. This marks the end of geological time periods usually.
Punctuated Equilibrium: Burst of evolutionary activity are followed by long periods of stability.
Niles Eldredge and Stephan Jay Gould proposed this in 1972.
Adaptive Radiation: Diversification of one ancestral species into many descendent species. New
species can live in many environments. Ex: Diversification of mammals