Day 14 March 6th Chapter 8

8/2/2019 Day 14 March 6th Chapter 8

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Day 14 March 6th Chapter 8

Final Chance to Make Up Second Exam Is noonFriday

(that means you have to find me, in person,and get the password and turn in your StudyGuide – be prepared!!!)



Mutation is theultimate source of

genetic variation in apopulation.



Nearly all mutations reduce anorganism’s 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?



8.8 Genetic drift is a random

change in allele frequenciesin a population.



Do you know what I’m talking about

when I say alleles?

1. Yes

2. No



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.





The important factor thatdistinguishes genetic drift from

natural selection:

The change in allele frequencies is not related to the alleles’ influence on

reproductive success.

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



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



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.



Two special cases of genetic drift, thefounder effect and population

bottlenecks, are important in the evolutionof populations.



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 “source” population, particularly if they are a smallsample.



Think GALAPAGOS!!!





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



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.



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.



Variation is necessary for natural selection



What’s your opinion?

1. I can see how different traits are passed from

parent to offspring.

2. I can not see how traits are passed from

parent to offspring.



Condition 1: Variation for a Trait

Variation is all around us.

Variation is the raw material on whichevolution feeds.



Condition 2: Heritability

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



Condition 3: Differential ReproductiveSuccess

1. There are more organisms born than can survive.




2. Organisms are continually struggling forexistence.

Question – should humans intervene in cases of extinction?




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



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.





At this point

1. I feel like I have a much better understanding

of how evolution works.

2. I understand that traits are passed from

parents to offspring, but I don’t think that’s

evolution.

3. I don’t get it at all. I can’t see how traits are

passed on from parents to offspring.



Most agricultural pests evolveresistance to pesticides.

How does this happen?

Winners versus Losers



Removing the Losers



Which trait in rabbits (listed below) hasevolved due to interactions with predators?

1. Speed

2. Coat color3. Eye color

4. 1 and 2

5. All of the above



Which trait in rabbits (listed below) hasevolved due to interactions with predators?

1. Speed

2. Coat color3. Eye color

4. 1 and 2

5. All of the above





“Survival of the Fittest”

Reproductive success

Fitness

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

reproductive output of individuals withalternative phenotypes



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?



The alleles carried by an individual

with high fitness will increase theirmarket share in a population over

time and the population will evolve.



There are three important elements to an

organism’s fitness:

1. An individual’s fitness is measuredrelative to other genotypes orphenotypes in the population.



There are three important elements to anorganism’s fitness:

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



There are three important elements to anorganism’s fitness:

3. Fitness depends on an organism’s

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.



"Survival of the fittest" is a

misnomer. Why?



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



Adaptation —the process by whichorganisms become better matched to theirenvironment and the specific features that

make an organism more fit —occurs as aresult of natural selection.



8.13 Natural selection does not lead toperfect organisms.



Why doesn’t natural selection leadto the production

of perfect organisms?



Factors that Prevent Populations fromProgressing Inevitably toward Perfection

1. Environments change quickly.

2. Variation is needed as the raw material of selection.

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

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Day 14 March 6th Chapter 8