Download Evolution of Populations - Sonoma Valley High School

Population
genetics
Population genetics
• In the early 1900’s
the science of
population genetics
was born.
• This science
explained the
relationship between
genetics and
evolution.
Wilhelm Weinberg
1862 - 1937
Genetic Equilibrium
• Population genetics
was an important
discovery because
populations are the
smallest unit that can
evolve.
• Traits within
populations show
variation.
Peppered moths
Think: What conditions would favor
black moths over white?
Variation Within A Population
• Some variations are
discontinuous.
– Ex: male Vs female
– Ex: Tall pea plants Vs short
pea plants.
• Some variations are
continuous.
– Polygenic traits usually
cause continuous traits
– Ex: human height
– Ex: human skin color
– Ex: size of fish in a pond.
Distribution of traits
• Continuous traits
demonstrate a bell
shaped curve
– Most individuals are
in “average”.
– Individuals with
“extreme” variation
are few in number.
think: Explain the change in the
graph after selection occurs.
Causes of Variation
• Traits are caused
by:
– Environment
– Heredity
• Usually both
factors play a
role.
Are these plants different heights
because of genetics or nutrition?
What Increases Variation?
3 causes of variation in a population.
1. Mutations to DNA.
2. Independent assortment & crossing over.
3. Random fertilization.
Allele Frequencies In A Gene Pool
•
Gene Pool;
–
•
All genes found in
an interbreeding
population.
Allele frequency;
–
% of a particular
allele in a
population.
Hardy-Weinberg Genetic Equilibrium
•
Allele frequencies
remain the same
generation after
generation.
•
This will be true
if 5 conditions
are met.
Flamingo population
Hardy-Weinberg Genetic
Equilibrium
1.
2.
3.
4.
5.
No change due to
mutations.
Individuals do not
move in or out of
the population.
The population is
and remains large.
Random mating.
No selection
Tule Elk population at Pt Reyes
Disruption of Genetic Equilibrium
•
If any of the 5
factors do not
occur, they can
cause the gene
frequency to
change in a
population.
•
If the gene
frequencies
change evolution
has occurred.
Tule Elk population at Pt. Reyes
Summary review
1. What is the shape of a
graph of normal
distribution?
2. What is a gene pool?
3. What are 3 causes of
genetic variation?
4. Given the
requirements of
genetic equilibrium do
populations remain
unchanged? Why?