10-23 Lecture Notes

7/30/2019 10-23 Lecture Notes

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ene ow an n ree ng

Todays questions:

I. How does ene flow cause chan es in allele frequencies?

II. How do inbreeding and other forms of non random mating cause changes in genotype frequencies?

III. How do inbreeding and the 4 evolutionary forces affect endangered species?


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I. How does gene flow change allele frequencies?

. eory: e one s an mo e

One way movement of individuals (and their alleles) from a large

Suppose that allele A 1 is at frequency 1.0 on the islandand that there are 400breeding individuals

Suppose that allele A 2 is at requency . on t e

continent (very large population)


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If 100 individuals move from the continent to the island and begin to breed, the frequencies of alleles

in the

island

population

are

now:

The Punchline:

fr(A1)=.8fr(A2)=.2

Allele frequency changes just like that.


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Different Species:

Speciations.

Population 1.

Inbreeding goes up.Drift goes up.Genetic variation goes down.Usually lowers fitness.

Population 2.Same.


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B. What are the evolutionary consequences of gene flow?

. , , more dissimilar, or no impact?

2. In the recipient population, does it increase fitness, decrease fitness, or no impact?

3. How is gene flow affecting human populations?

It makes them more alike, it homogenizes them.

It is random with respect to fitness (if we don't know the situation),though usually, it'll lower fitness because populations receiving gene flowis well adapted to environment in most cases. Opposite scenario can alsoapply, where if the receiving population is not well adapted to theirenvironment.

We're creating new genotypes through interracial marriage between differentpopulations. Massive gene flow with immigration and emigration. Allelefrequencies are becoming more alike globally.


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II. How do inbreeding and other forms of non random matin cause chan es in enot e fre uencies?

Consider selfingan extreme form of inbreeding1 1 1 2

1. How does inbreeding affect allele frequencies?

2. How does inbreeding affect genotype frequencies? It keeps it the same.

It vastly affects it, homozygotes increase, heterozygotes decrease.


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3. Why does inbreeding depression occur?

Deleterious recessives

are

usually

at

low

frequency,

so

most are found in

BUT, inbreeding increases the proportion of homozygous recessive individuals, so

Observed in humans, many other animals, many plants.

Heterozygotes.

More individuals are lower in fitness.


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4. Inbreeding does not change allele frequencies by itself, but it makes selection (against deleterious recessives) more efficientmeaning that allele frequencies change faster.

Explain what this statement means, and why it is correct. It allows for recessive allele to be vulnerable to selection because thedeleterious trait is now expressed and can be acted upon by naturalselection.


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III. How do inbreeding and the 4 evolutionary forces affect endangered species?

1. Amur leopards: a distinct subspecies (large bodied, light color in winter, heavy

coat


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Hunting and habitat destruction have reduced Amur leopards to ~20 individuals in the wild. Mutation, drift, and

inbreeding may

be

reducing

average

fitness.

Geneticall , ca tive o ulations in Ja an and elsewhere are a mlange of different source populations/subspecies. Phenot icall the ca tive o ulations are distinct from the Amur population (smaller, less dense fur). Climate chan e ma be im actin the current ran e of

Amur leopards.

introduced to

the

wild,

to

augment

the

Amur

population?


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Pros:

Cons:


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2. Prairie chickens in Illinois

In small, isolated populations, document steady fitness declines over time.

In 1992 biolo istsreleasedindividuals

brought in fromSouth Dakota.


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Interpret this graph

d

h a t c h

% e

g g s

Year

10-23 Lecture Notes

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