Transcript Lecture Chpt. 24 Evolutn Show 4 Variatn

On truth in Biology :
"the only thing always true in biology is
that there are always exceptions..."
Dr. Rita Calvo
Cornell University
microevolution
microevolutio
microevoluti
microevolut
Microevolution:
generation-to- generation
in allele or
genotypic frequencies.
*genetic
changes in a
gene pool*
changes
look, it’s
Jennifer!
Microevolution:
allele or genotypic
frequency changes…
HOW????
1) Mutations… of germ cells
(those that produce gametes!!!)
Microevolution:
allele or genotypic
frequency changes…
HOW????
Point mutations
translocations
Gene duplication ex. Gene for smell
Jumping genes
Microevolution:
allele or genotypic
frequency changes…
HOW????
2) Sexual
recombination
QuickTime™ and a
decompressor
are needed to see this picture.
BIG
Microevolution
causes:
BIG Microevolution
causes:
1) Genetic drift random, evolutionary
changes in small populations due to chance… not due to
natural selection!!!
The genes of the next generation will be the genes of the “lucky”
individuals, not necessarily the healthier or “better” individuals.
QuickTime™ and a
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If the gene for green coloration drifts out of the population, the gene
is gone for good—unless, of course, a mutation or gene flow
reintroduces the green gene.
QuickTime™ and a
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the most important effects of genetic drift: it reduces the amount of
genetic variation in a population. And with less genetic variation,
there is less for natural selection to work with. If the green gene
drifts out of the population, and the population ends up in a situation
where it would be advantageous to be green, the population is out of
luck. Selection cannot increase the frequency of the green gene,
because it’s not there for selection to act on. Selection can only act
on what variation is already in a population; it cannot create
variation.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
BIG Microevolution
causes:
1) Genetic drift (the smaller the sample, the quicker
& more drastic the change effect!
greater the chance of deviations
from the expected probability.)
BIG Microevolution
causes:
Genetic drift -
Population must be large
in order to rule out
changes due to chance as
an agent of evolution
BIG Microevolution
causes:
Genetic drift -
The larger the population,
the more closely related
the genes will resemble
the previous population.
1) BOTTLENECK EFFECT
Certain alleles become
under-represented
Where did the
white ones go?
1) BOTTLENECK EFFECT
Some alleles are
eliminated altogether
Where did the
orange ones go?
1) BOTTLENECK EFFECT
Some alleles are
overrepresented
Are there
proportionally
more blue ones
now?
1) BOTTLENECK EFFECT
• Reduction of population size
may reduce gene pool for
evolution to work with
• ex.CHEETAHS
• Some genes
are not
represented
anymore
QuickTime™ and a
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BOTTLENECK EFFECT
New
colony
FOUNDERS EFFECT
Disproportionate
New
colony
New colony
FOUNDERS EFFECT
• Genetic drift in a new colony
that separates from a parent
population.
• Reduces genetic
variability
• ex.
Old-Order Menonite ~
hearing disorder
FOUNDERS
EFFECT
BIG Microevolution
causes:
2) Gene flow (also called migration)
any movement of genes from one population to another.
Gene flow includes many different kinds of events:
pollen being blown to a new destination or
people moving to new cities or countries.
If genes are carried to a population where those genes
previously did not exist, gene flow can be a very
.
important source of genetic variation
BIG Microevolution
causes:
2) Gene flow
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
BIG Microevolution
causes: Gene flow QuickTime™ and a
decompressor
are needed to see this picture.
BIG Microevolution causes:
Nonrandom mating - select a
mate based upon phenotype (and
what they smell like… hmmmm)
BIG Microevolution causes:
Nonrandom mating - select a
mate based upon phenotype (and
what they smell like… hmmmm)
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_08.html
BIG Microevolution
causes: 4) Natural Selection -
over generations, the proportion of
favorable
alleles
survive.
All individuals are not equal in their
ability to survive & reproduce
Different ways this happens:
 characteristics vary: Within the
Population
Genetic Variation =
 Within the Population -
phenotypic
polymorphism
phenotypic
polymorphism
Garter Snakes
Gaillardia
genotypic
polymorphism
Genetic Variation
 Between Populations - Clinal
Along a geographic axis
Selection of genetic variation
N. Selection of genetic
variation Here is the base-line:
Selection of genetic
variation
 stabalizing
selection:
ex. Birth weight in babies
Selection of genetic variation
 Stabalizing selection:
•Elimination of extreme
phenotypes.
Favors intermediate
This reduces variation

Selection of genetic variation
 Directional Selection:
ex. Galapagos Island finch beak size
Selection of genetic variation
 Directional Selection:

Elimination of intermediate
phenotypes.
Favors the rare

This reduces variation
Selection of genetic variation
Diversifying Selection:
Selection of genetic variation
Diversifying Selection:
Elimination of intermediate
phenotypes.


Favors the extremes.

This reduces variation
Question
• Does evolution result in perfect organisms?
Misconception: “Natural
selection gives organisms
what they ‘need.’ ”
Summary
• Know the difference between a
species and a population.
• Know that the unit of
evolution is the population
and not the individual.
Summary
• Know the H-W equations
and how to use them in
calculations.
• Know the H-W assumptions
and what happens if each is
violated.
Summary
• Identify various means to
introduce genetic variation
into populations.
• Know the various types of
natural selection.