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Genetic Variation
 When we picture penguins we imagine them all the
same. Perfect little carbon copies, genetic clones of
black and white, wobbly, birdlike creatures that like
ice. They vary greatly, however, when you take a closer
look.
Genetic Variation
 Increases the chance that some individuals will
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survive.
Phenotypes are all of an organisms physical
characteristics.
Penguins – wing size, height, roundness, feather
patterns, coloring….etc
The greater the variation in phenotypes, the higher the
probability of survival during environmental changes.
Short penguins can stay warmer more easily than taller
penguins and would survive extremely cold winters.
Genetic Variation
 In warmer weather, tall, slim penguins would be better
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divers and could catch more fish easily.
Genetic variation is stored in a populations gene
pool.
A gene pool is the combined alleles of all of the
individuals in a population.
Each allele exists at a certain rate, or frequency.
An allele frequency is a measure of how common a
certain allele is in the population.
Word origins
 Pool - comes from the old french word poule. This
means chicken…but poule comes from the Latin word
pullus….the young of an animal.
Allele Frequency
 Count the number of times that an allele occurs in a
population then divide that by the total number of
alleles.
 For example. If there are 8 green frogs and 5 brown
frogs in a population, the allele frequency for green is
8/13 and the allele frequency for brown is 5/13.
Genetic Variation
 Comes from two main sources: mutation and
recombination.
 Mutation is a random change in the DNA of a gene.
 Recombination occurs during meiosis primarily.
When gametes are made, each parents alleles are
arranged in new ways. This shuffling results in
different combinations.
Hybridization
 The crossing of two different species that share
common genes.
Questions
 Natural Selection acts on _________
 Phenotypes
 Why does genetic variation increase the chance that
some individuals in a population will survive?
 Genetically diverse populations display high
phenotypic variation. If some individuals had a
resistance to a certain disease, then that small
phenotype would survive.
Questions
 If a certain traits allele frequency is 100 percent,
describe the genetic variation.
 There is no genetic variation.
Questions
 What might cause mutation?
 Exposure to radiation, insertions, deletions,
unavailable resources.
 http://en.wikipedia.org/wiki/Mutation
Distributions
 Normal distribution - a type of distribution of
phenotypes in which the frequency is highest near the
mean value and lowest toward each extreme end.
Microevolution
 The observable change in the allele frequencies of a
population over time.
 Natural selection can change the distribution of a trait
along one of three paths: directional, stabilizing, or
disruptive selection.
Directional Selection
 A type of selection that favors phenotypes at one
extreme.
 This will cause a shift in the phenotypic distribution.
The mean will move over to the extreme value.
Use the
Example of
Bacteria and
Resistance to
Antibiotics.
Stabilizing Selection
 The intermediate phenotype is favored and becomes
the most common in a population.
 Gall flies lay their eggs in the shoots of a plant called
goldenrod.
 Downy woodpeckers attack larger galls and feed on the
larvae inside.
 The wasp lays its own eggs inside small galls. After the
wasp larvae emerge from the eggs, they eat the gall fly
larvae.
Stabilizing Selection
 This means that the large and small gall formations are
killed and the medium sized gall fly will survive.
 Note that the selection against both extremes
decreases genetic diversity.
Disruptive Selection
 Occurs when both extreme phenotypes are favored.
 By favoring both extremes, this is how new species are
developed.