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I. Introduction
A. Variations of Traits
II. Variation
A. Where do variations come from?
1. Genetic Recombinations
2. Reproductive Recombinations
3. Mutations
B. How are variations maintained?
1. Gene Pool
a. The frequency of traits (carried on
genes) in a population stays the same
unless something atypical occurs to
change them.
b. Evolution can be defined as a change in
the frequency of traits in the gene pool.
2. The Hardy-Weinberg Equilibrium Equation
a. An equation that can be used to model
the changes in a gene pool.
p + q = 1
p2 + 2pq + q2 = 1
AA Aa aA aa
C. Where do changes in the gene pool originate?
1. Anything that changes the normal genetic
interactions can have an effect on the gene
pool.
III. Changes in the Gene Pool
A. Mutation
1. A change in the genetic makeup of an
organism.
2. Harmful Mutations
3. Neutral Mutations
4. Advantageous Mutations
B. Gene Flow
1. Migration
a. Immigrants add genes to a population.
b. Emigrants take genes away from a
population.
C. Genetic Drift
1. Bottleneck Effect
a. A reduction in the population limits the
numbers of genes present.
2. Founder Effect
a. New populations derived from only a
few immigrants have gene frequencies
that differ from the original population.
D. Nonrandom Mating
1. Abnormal mating patterns can affect the
frequency of genes in a population.
2. Reproductive Isolation of Subpopulations
a. Temporal: mating at different times
b. Behavioral: correct mating cues not
given
c. Mechanical: body parts do not match
d. Gametic: sperm and egg do not match
e. Geographical: subpopulations are
physically separated and cannot mate
E. Natural Selection
1. Changes in the environment can "select"
certain traits because those traits allow the
organism to survive better in the new
environment.
IV. Speciation
A. Species Definition
1. Species are groups of potentially
interbreeding natural populations which are
reproductively isolated from other such
groups (that is, they normally would not
breed with each other and produce viable
offspring).
B. Sympatric Speciation
1. Occurs when subpopulations exist in the
same area.
2. Usually occurs because of increases in
chromosome numbers.
a. Common in plants; rare in animals.
C. Allopatric Speciation
1. Often occurs when geographic changes
occur to separate parts of the population.
2. Most common type of speciation.
D. Rates of Speciation
1. Gradual
2. Punctuated Equilibrium
V. Summary
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