on truth in biology : "the only thing always true in biology is that there are always...

On truth in Biology :

"the only thing always true in biology is that there are

always exceptions..."

Dr. Rita CalvoCornell University

microevolutmicroevoluti

microevolutio

microevolution

Microevolution:Microevolution: generationgeneration--toto- -

generationgeneration changeschanges in in alleleallele or or genotypic genotypic frequencies.frequencies.*genetic *genetic changes in a changes in a

gene poolgene pool**look, it’s Jennifer!

Microevolution:Microevolution: alleleallele or or

genotypic genotypic frequency changes…frequency changes…HOW????HOW????

1) Mutations… of germ cells

(those that produce gametes!!!)


genotypic genotypic frequency changes…frequency changes…HOW????HOW????

Point mutationstranslocations

Gene duplication ex. Gene for smell

Jumping genes


genotypic genotypic frequency changes…frequency changes…HOW????HOW????2) Sexual

recombination

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BIGBIG Microevolution Microevolution

causes:causes:

BIG BIG Microevolution Microevolution

causes:causes:1) Genetic drift -

randomrandom, , evolutionary evolutionary changeschanges in small populations - due to due to chancechance… not due to natural selection!!!

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The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals.



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.



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.


causes:causes:1) Genetic drift -(the smaller the sample,

the quicker & more drastic the change effect! greater the chance of deviations from the expected

probability.)


causes:causes:Genetic drift -

Population must be Population must be largelarge in order to in order to rulerule outout changes changes

due to chance as an due to chance as an agent of evolutionagent of evolution


causes:causes:Genetic drift -

The larger the population, the more closely

related the genes will resemble the

previous population.

1) BOTTLENECK EFFECT1) BOTTLENECK EFFECT


Certain alleles become under-represented

Where did the white ones go?


Some alleles are eliminated altogether

Where did the orangeorange ones go?


Some alleles are overrepresented

Are there proportionally more blue ones now?

BOTTLENECK EFFECTBOTTLENECK EFFECT

• Reduction of population size may reduce gene pool for

evolution to work with•ex.CHEETAHSex.CHEETAHS•Some genes Some genes are not are not

represented represented anymoreanymoreQuickTime™ and a

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FOUNDERS EFFECTFOUNDERS EFFECT

New colony

FOUNDERS EFFECTFOUNDERS EFFECT

New colony

Disproportionate

New colony

FOUNDERS FOUNDERS EFFECTEFFECT

•Genetic drift in a new colony that separates from a parent population.

•Reduces genetic variability

•ex. Old-Order Menonite ~ hearing disorder


causes: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.


causes:causes: 2) Gene flow




causes:causes: Gene flow -

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BIG Microevolution BIG Microevolution causes:causes: Nonrandom mating - select a mate based upon phenotype (and what they smell like… hmmmm)

BIG Microevolution BIG Microevolution causes: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 BIG Microevolution Microevolution causes: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 Genetic Variation =Variation =

Within the Population -

phenotypic phenotypic polymorphismpolymorphism

Garter Snakes Gaillardia

phenotypic phenotypic polymorphismpolymorphism

genotypic genotypic polymorphismpolymorphism

Genetic Genetic VariationVariation

Between Populations - Clinal

Along a geographic Along a geographic axisaxis

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

•Elimination of

extreme phenotypes. Favors

intermediate This reduces variation

Selection of genetic Selection of genetic variationvariation

Stabalizing selection:


Directional Selection:

ex. Galapagos Island finch beak size

Elimination of

intermediate phenotypes.

Favors the rare This reduces variation


Directional Selection:

Selection of genetic Selection of genetic variationvariation Diversifying Selection:

Elimination of intermediate phenotypes.

Favors the extremes.

This reduces variation

Selection of genetic Selection of genetic variationvariation Diversifying Selection:

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.

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