Transcript Ch. 16 Genetic Equilibrium and Selection

Chapter 16-1
Genetic Equilibrium
Reminder- This will be up
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Population Genetics
• The study of evolution from a genetic
point of view.
Bell Curve
Natural Selection acts on
Variations
Quantitative traits, such as height and
weight, tend to follow a bell shaped
curve.
Examples of Bell Curves
Variations in a Population
A. Some variations are influenced by
environmental factors, such as the
amount of food or quality of food
available to an organism.
B. Variations are also
influenced by heredity.
What Variations do you see in our
classroom population???
Variation in Genes
A. Mutation- a random change in a gene
that is passed on to offspring.
B. Recombination- the reshuffling of genes
in a diploid individual (meiosis;
independent assortment crossing over)
C. The random pairing of gametes during
sexual reproduction.
Gene Pool
• The total genetic information in a
population.
(the genes for the next generation exist
in an imaginary pool)
Allelic Frequency
• The percentage of any specific allelle in
the gene pool
Genetic Equilibrium
• A population in which the allele
frequencies stay the same
Population
• A population consists of a group of
individuals of the same species that
routinely interbreed.
Population of Giraffes in Calauit in the Philippines
Populations and Evolution
• Populations are important
in the study of evolution
because a population is
the smallest unit in which
evolution occurs
Populations evolve, not
individuals!!!
Microevolution
• A change in the collective
genetic material of a
population. (genetic
material= the many alleles
or variations of the many
genes that code for various
traits)
How can a population’s gene
pool change over time?
When a population is not in genetic
equilibrium….
16.2 Disruptions in Genetic
Equilibrium
1. Mutations
2. Genetic Drift in Small populations
3. Gene Flow
– Immigration- the movement of individuals
into a population.
– Emigration- the movement of individuals
out of a population.
4. Non-random mating
5. Natural Selection
Genetic Drift
Genetic drift is the phenomenon by which
allele frequencies in a population change
as a result of random events, or chance.
e.g. Northern elephant seals
have lost genetic
variability because they
have been hunted to near
extinction. With such a
small population left and a
small gene pool less
variation.
Genetic Bottleneck
Occurs when environmental
disturbances cause populations to
become so small that inbreeding
occurs.
– leads to decreased genetic variability.
– Over evolutionary time, populations with low
variability are less likely to adapt to changing
environmental conditions.
• e.g. Cheetahs and black footed ferrets.
3 Different Types of Selection
• Stabilizing
• Directional
• Disruptive
Stabilizing Selection
• Individuals with the average form of the
trait have the highest fitness
Directional Selection
• Individuals that display one of the
extreme forms of trait have greater
fitness than individuals with an average
form of the trait.
Disruptive Selection
• Individuals with either extreme of a trait
have greater fitness than the average
form of the trait
Journal:
• If the largest and smallest organisms in
a population have more success in their
ability to reproduce, this might lead to
what type of selection?
16.3 Speciation
• The process of species formation which
results in closely related species.
What can cause speciation?
• Geographic Isolation
• Reproductive Isolation
Cause of Speciation
• Geographical Isolation: the physical
separation of members of a population.
e.g. Death Valley pupfish
Grand Canyon squirrels
Cause of Speciation
• Reproductive Isolation: results from
barriers to successful breeding between
population groups in the same area.
e.g. Frogs
The Rates of Speciation
• Gradualism
• Punctuated Equilibrium
• The End