Download Disruption of Genetic Equilibrium

Disruption of Genetic
Equilibrium
Objectives
 List the five conditions that cause evolution
to occur
 Describe stabilizing, directional, disruptive,
and sexual selection
Introduction
 Evolution is the change in the population’s
genetic material over generations
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Population’s allele or genotype frequencies change
Any violation of the conditions necessary for HardyWeinberg can result in evolution
 Five conditions that cause evolution to occur
 Mutation
 Migration
 Genetic Drift
 Nonrandom Mating
 Natural Selection
Mutation
 Mutations are changes in
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DNA sequences
Mutations occur
constantly but at a very
low rate under normal
conditions
Exposure to mutagens
(mutation-causing
agents) can increase
mutation rates
Most mutations are
harmful
Beneficial mutations are
an important part of
evolution
Migration
 Immigration is the movement
of individuals into a
population
 Emigration is the movement
of individuals out of a
population
 Immigration and emigration
can change gene frequencies
 Gene flow is the process of
genes moving from one
population to another
Genetic Drift
 Genetic drift is where allele frequencies in a
population change as a result of random events
 Genetic drift can occur in small populations
when an allele becomes more or less common
 Genetic drift can be caused by:
 An individual in a small population carrying a
particular allele and having more decedents that
other individuals
 Founder effect: when a small group of
individuals colonizes a new habitat
Nonrandom Mating
 Many species do not mate
randomly
 Mate selection is often
influenced by geographic
proximity
 Assortative mating is the
selection of a mate based
similarity of characteristics
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Mate probably has similar genes
Can result in offspring with
disorders caused by recessive
genes
Natural Selection
 Most significant factor that disrupts genetic
equilibrium
 The most fit members of a population pass on
their genetics to the next generation
 4 Main Types of Natural Selection
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Stabilizing Selection
Directional Selection
Disruptive Selection
Sexual Selection
Stabilizing Selection
 Individuals with the
average form of a trait
have the highest fitness

Individuals in the middle of
the bell curve
 Extreme forms of a trait
lower the fitness of the
individual

Example: A lizard that is too
big is easily spotted and killed
by a predator. A lizard that is
too small is too slow to escape
a predator.
Directional Selection
 Individuals that display a more extreme form
of a trait have greater fitness than individuals
with an average form of the trait
 Individuals at one end of the curve have a
higher fitness those individuals in the middle
or at the other end
Disruptive Selection
 Individuals with either extreme variation of a
trait have greater fitness than individuals
with the average form of the trait
 Individuals at the upper and lower ends of the
curve have a higher fitness those individuals
near the middle
Sexual Selection
 Females choose the males
they mate with based on
certain traits
 Extreme traits indicate
quality of genes
 Example: Female deer
choose males with the
biggest antlers. However, big
antlers make the males
easier to see by predators. As
long as the male survives
long enough to reproduce,
his genes will be passed on.
Notes Review
 List the five conditions that cause evolution
to occur





Mutation
Migration
Genetic Drift
Nonrandom Mating
Natural Selection
Notes Review
 Describe stabilizing, directional, disruptive,
and sexual selection
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Stabilizing Selection: Individuals with the average
form of a trait have the highest fitness
Directional Selection: Individuals that display a more
extreme form of a trait have greater fitness than
individuals with an average form of the 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