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Population Evolution

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Bio Prezis SPSCepiel

on 12 February 2017

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Transcript of Population Evolution

population evolution

Definition of a population
Population: a group of organisms
that are the same species and live in the same place at the same time.
Another important term in
populations is gene pool.
Gene pool is the total collection
of genes in a population.
gene pool
is all alleles (remember big B and little b?)
in the population. As the FREQUENCIES of these alleles
change in a population, you get
. This is the
smallest scale of evolution.
Genetic Variation is the piece
of evolution that Darwin was missing. Gregor Mendel discovered
this genetic variation and that it was passed to offspring from parents.
What accounts for
genetic variation?
Write down the ways that genetic
variation is created.
What allows for genetic variation?
(in case you forgot!)
1. Mutations: a change in the DNA
1 in every 100,000 genes
2. Sexual Reproduction: unique combo of alleles
from an organism's parents.
random fertilization
crossing over
independent assortment
Why do we care about genes when we
talk about evolution? How are they
related? (put it all together)
The genetic variation in a gene pool
allows for new and different traits
to appear in an organism. This change in
gene frequencies allows for something
. Any introduction or
deletion of alleles from a population can
lead to changes in the population.
Mechanisms of Microevolution

1. Natural Selection
The ENVIRONMENT comes into play because it will favor certain traits over others.
Example: Peppered Moth
3. Genetic Drift
A change in the gene pool due to a chance event.
2 examples:
Bottleneck Effect: a large flood wipes out most of a population and the remaining organisms have a smaller gene pool.
Founder Effect: a few individuals of a population colonize an island. The smaller group has a smaller gene pool. The Galapagos Finches are an example.
2. Gene Flow
Allele frequencies change as individuals move into and out of the population.
Example: Humans move all over the world today and this introduces new alleles to the population
4. Mutation
Has a very small effect on changing allele frequencies because
mutations are rare and random.
Natural Selection is the only mechanism of microevolution that will improve a population's survival in an environment.
Chance: DNA in the population
Sorting: some of these traits are favored in a certain environment.

The individuals that have the "BEST FIT" with their environment will have the highest FITNESS.
They will be able to produce the most viable, fertile offspring and pass their genes on to the next generation.
Now that we understand biological fitness, what is missing in the phrase "survival of the fittest."
Stabilizing Selection
: favors the intermediate phenotypes. Not a lot of variation in phenotypes.
Directional Selection
: Shifts the phenotype in one direction as this phenotype is favored by the environment. Often occurs when the environment changes or the organism moves to a new environment.
Disruptive Selection:
Phenotypes at both extremes are favored.
Example: Human birth weight.
Example: Industrial melanism (the peppered moth).
Example: White and Black snails in a
speckled environment.
One more type of selection:
Sexual Selection
individuals with certain characteristics are more likely than others to obtain mates.
Example: Showy feathers on a male bird.
One final question:
Why doesn't natural selection eliminate unfavorable genotypes and reduce genetic variation?
Types of Selection
Gene pool
One more Mechanism
Natural selection occurs as the "fittest" members of the population survive. It is the PHENOTYPE of the organism that interacts with the environment and determines its survival.
Several common patterns of natural selection
Check yourself:
Explain each of these pictures.
Learning Goals:
1. Explain how genetic variation impacts evolution.
2. Relate biological fitness to natural selection.
3. Differentiate between the types of microevolution and how they apply to real world situations.

Check yourself
Which type of microevolution is in this example?
On the small Micronesian island of Pingelap in the Western Pacific, a typhoon killed at least 90% of its people. One of the 20 survivors was a man named Nahnmwarki Mwanenised. He had achromatopsia, a very rare genetically inherited recessive eye condition that causes total color blindness and extreme sensitivity to light. Six generations later, nearly 5% of the island's population had achromatopsia. By comparison, only 1 in 33,000 people in the United States have it.
Check yourself:
1. Why was the idea of sexual selection so difficult people during Darwin's time to accept?
2. Explain how the large, heavy tail actually improves the survival of the POPULATION.
Genetic Drift
Gene flow
Bottleneck Effect
Founder Effect
Sexual Selection
Directional Selection
Disruptive Selection
Natural Selection
Allelic Frequencies
Stabilizing Selection
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