day 15 october 17th chapter 8 scribd

8/3/2019 Day 15 October 17th Chapter 8 Scribd

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Day 15 October 17th Chapter 8

Mutations and Alleles and Genetic

drift

OH MY!!!


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Mutation is theultimate source of

genetic variation in apopulation.


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Nearly all mutations reduce anorganisms fitness.

Suppose that you have written a ten-pagepaper.

Randomly select one letter in the paperand change it to another letter

Is the change more likely to make yourpaper better or worse?


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8.8 Genetic drift is a random

change in allele frequenciesin a population.


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Alleles

An allele is an alternative form of a gene (onemember of a pair) that is located at a specificposition on a specific chromosome.

These DNA codings determine distinct traits thatcan be passed on from parents to offspring.


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The important factor thatdistinguishes genetic drift from

natural selection:

The change in allele frequencies isnotrelated to the alleles influence on

reproductive success.


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The impact of genetic drift ismuch greater in small

populations than in largepopulations.


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The important factor thatdistinguishes genetic drift from

natural selection:

The change in allele frequencies isnotrelated to the alleles influence on

reproductive success.

Like, having a cleft chin does not help you to reproduce


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The impact of genetic drift ismuch greater in small

populations than in largepopulations.

Like in the case of orange-furred tigers versus white-furred tigers


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Fixation

Genetic drift can lead to fixation for oneallele for a gene in a population.

If this happens, there is no morevariability in the population for this gene.

Genetic drift reduces the geneticvariation in a population.


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Two special cases of genetic drift, thefounder effect and population

bottlenecks, are important in the evolutionof populations.


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Founder Effect

A small number of individuals may leave apopulation and become the foundingmembers of a new, isolated population.

The founders may have different allelefrequencies than the original sourcepopulation, particularly if they are a smallsample.


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Think GALAPAGOS!!!


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Why are Amish people more likely to haveextra fingers and toes?


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8.9 Migration into or

out of a populationmay change allelefrequencies.

Migration, also called geneflow, is the movement of

some individuals of a speciesfrom one population toanother.


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8.10 When three simple conditions aresatisfied, evolution by natural selection

occurs.1. There must be variation for the particular trait

within a population.

2. That variation must be inheritable.

3. Individuals with one version of the trait mustproduce more offspring than those with a

different version of the trait.


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Variation is necessary for natural selection


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Condition 1: Variation for a Trait

Variation is all around us.

Variation is the raw material on whichevolution feeds.


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Condition 2: Heritability

We call the transmission of traits from parents to theirchildren through genetic information inheritance orheritability.


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Condition 3: Differential ReproductiveSuccess

1. There are more organisms born than cansurvive.


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2. Organisms are continually struggling forexistence.

Question should humans intervene in cases of extinction?


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3. Some organisms are more likely to winthis struggle and survive and reproduce.


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Differential Reproductive Success

From all the variationexisting in a population,individuals with traits

most suited toreproduction in theirenvironment generallyleave more offspring than

individuals with othertraits.


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Most agricultural pests evolveresistance to pesticides.

How does this happen?

Winners versus Losers


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Removing the Losers


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Survival of the Fittest

Reproductive success

Fitness

a measure of the relative amount ofreproduction of an individual with a particularphenotype, as compared with the

reproductive output of individuals withalternative phenotypes


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Fruit Fly Example

One fly carries the genes for a version of atrait that allows it to survive a long timewithout food.

The other fly has the genes for a differentversion of the trait that allows it to survive

only a short while without food.

Which fly has the greater fitness?


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The allelescarried by an individualwith high fitness will increase their

market share in a population overtime and the population will evolve.


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There are three important elements to an

organisms fitness:

1. An individuals fitness is measuredrelative to other genotypes orphenotypes in the population.


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There are three important elements to anorganisms fitness:

2. Fitness depends on the specificenvironment in which the organism lives.


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There are three important elements to anorganisms fitness:

3. Fitness depends on an organisms

reproductive success compared to otherorganisms in the population.

If you are sterile, and can never have babies, your fitness is ZERO

On the other hand, if you inherit an allele that gives you a trait that

causes you to die at half the age of everyone else, but also causes

you to have twice as many offspring as the average while you are

alive, your fitness is increased.


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"Survival of the fittest" is a

misnomer.Why?


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8.12 Organisms in a population can becomebetter matched to their environment throughnatural selection.


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Take-home message 8.12Adaptationthe process by which

organisms become better matched to theirenvironment and the specific features that

make an organism more fitoccurs as aresult of natural selection.


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8.13 Natural selection does not lead toperfect organisms.


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Why doesnt natural selection leadto the production

of perfect organisms?


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Factors that Prevent Populations fromProgressing Inevitably toward Perfection

1. Environments change quickly.

2. Variation is needed as the raw material ofselection.

3. There may be multiple different alleles for atrait, each causing an individual to have thesame fitness.

day 15 october 17th chapter 8 scribd

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