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Measuring Evolution of Populations. 5 Agents of evolutionary change. Mutation. Gene Flow. Non-random mating. Genetic Drift. Selection. Populations & gene pools. Concepts a population is a localized group of interbreeding individuals

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Measuring Evolution of Populations

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Measuring evolution of populations

MeasuringEvolution of Populations


5 agents of evolutionary change

5 Agents of evolutionary change

Mutation

Gene Flow

Non-random mating

Genetic Drift

Selection


Populations gene pools

Populations & gene pools

  • Concepts

    • a population is a localized group of interbreeding individuals

    • gene pool is collection of alleles in the population

      • remember difference between alleles & genes!

    • allele frequencyis how common is that allele in the population

      • how many A vs. a in whole population


Evolution of populations

Evolution of populations

  • Evolution = change in allele frequencies in a population

    • hypothetical: what conditions would cause allele frequencies to not change?

    • non-evolving population

      REMOVE all agents of evolutionary change

      • very large population size (no genetic drift)

      • no migration (no gene flow in or out)

      • no mutation (no genetic change)

      • random mating (no sexual selection)

      • no natural selection (everyone is equally fit)


Hardy weinberg equilibrium

Hardy-Weinberg equilibrium

  • Hypothetical, non-evolving population

    • preserves allele frequencies

  • Serves as a model (null hypothesis)

    • natural populations rarely in H-W equilibrium

    • useful model to measure if forces are acting on a population

      • measuring evolutionary change

G.H. Hardy

mathematician

W. Weinberg

physician


Hardy weinberg theorem

Hardy-Weinberg theorem

  • Counting Alleles

    • assume 2 alleles = B, b

    • frequency of dominant allele (B) =p

    • frequency of recessive allele (b) = q

      • frequencies must add to 1 (100%), so:

        p + q = 1

BB

Bb

bb


Hardy weinberg theorem1

Hardy-Weinberg theorem

  • Counting Individuals

    • frequency of homozygous dominant: p x p = p2

    • frequency of homozygous recessive:q x q = q2

    • frequency of heterozygotes: (p x q) + (q x p) = 2pq

      • frequencies of all individuals must add to 1 (100%), so:

        p2 + 2pq + q2 = 1

BB

Bb

bb


H w formulas

B

b

BB

Bb

bb

H-W formulas

  • Alleles:p + q = 1

  • Individuals:p2 + 2pq + q2 = 1

BB

Bb

bb


Using hardy weinberg equation

Using Hardy-Weinberg equation

population: 100 cats

84 black, 16 white

How many of each genotype?

q2 (bb): 16/100 = .16

q (b): √.16 = 0.4

p (B): 1 - 0.4 = 0.6

p2=.36

2pq=.48

q2=.16

BB

Bb

bb

What are the genotype frequencies?

Must assume population is in H-W equilibrium!


Using hardy weinberg equation1

BB

Bb

bb

Using Hardy-Weinberg equation

p2=.36

2pq=.48

q2=.16

Assuming H-W equilibrium

BB

Bb

bb

Null hypothesis

p2=.20

p2=.74

2pq=.64

2pq=.10

q2=.16

q2=.16

Sampled data

How do you explain the data?

How do you explain the data?


Application of h w principle

Application of H-W principle

  • Sickle cell anemia

    • inherit a mutation in gene coding for hemoglobin

      • oxygen-carrying blood protein

      • recessive allele = HsHs

        • normal allele = Hb

    • low oxygen levels causes RBC to sickle

      • breakdown of RBC

      • clogging small blood vessels

      • damage to organs

    • often lethal


Sickle cell frequency

Sickle cell frequency

  • High frequency of heterozygotes

    • 1 in 5 in Central Africans = HbHs

    • unusual for allele with severe detrimental effects in homozygotes

      • 1 in 100 = HsHs

      • usually die before reproductive age

Why is the Hs allele maintained at such high levels in African populations?

Suggests some selective advantage of being heterozygous…


Malaria

Malaria

Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells

1

2

3


Heterozygote advantage

Heterozygote Advantage

  • In tropical Africa, where malaria is common:

    • homozygous dominant (normal)

      • die or reduced reproduction from malaria: HbHb

    • homozygous recessive

      • die or reduced reproduction from sickle cell anemia: HsHs

    • heterozygote carriers are relatively free of both: HbHs

      • survive & reproduce more, more common in population

Hypothesis:

In malaria-infected cells, the O2 level is lowered enough to cause sickling which kills the cell & destroys the parasite.

Frequency of sickle cell allele & distribution of malaria


Measuring evolution of populations

Any Questions??

Any Questions??

Any Questions??


Measuring evolution of populations

Mutation

Gene Flow

Non-random mating

Genetic Drift

Selection

Hardy-WeinbergLab Data


Hardy weinberg lab equilibrium

Hardy Weinberg Lab: Equilibrium

Original population

Case #1 F5

18 individuals

36 alleles

p (A):0.5

q (a):0.5

total alleles = 36

p (A): (4+4+7)/36 = .42

q (a): (7+7+7)/36 = .58

AA

4

Aa

7

aa

7

AA

.25

Aa

.50

aa

.25

AA

.22

Aa

.39

aa

.39

How do you explain these data?


Hardy weinberg lab selection

Hardy Weinberg Lab: Selection

Original population

Case #2 F5

15 individuals

30 alleles

p (A):0.5

q (a):0.5

total alleles = 30

p (A): (9+9+6)/30 = .80

q (a): (0+0+6)/30 = .20

AA

9

Aa

6

aa

0

AA

.25

Aa

.50

aa

.25

AA

.60

Aa

.40

aa

0

How do you explain these data?


Hardy weinberg lab

Heterozygote Advantage

Hardy Weinberg Lab:

Original population

Case #3 F5

15 individuals

30 alleles

p (A):0.5

q (a):0.5

total alleles = 30

p (A): (4+4+11)/30 = .63

q (a): (0+0+11)/30 = .37

AA

4

Aa

11

aa

0

AA

.25

Aa

.50

aa

.25

AA

.27

Aa

.73

aa

0

How do you explain these data?


Hardy weinberg lab1

Heterozygote Advantage

Hardy Weinberg Lab:

Original population

Case #3 F10

15 individuals

30 alleles

p (A):0.5

q (a):0.5

total alleles = 30

p (A): (6+6+9)/30 = .70

q (a): (0+0+9)/30 = .30

AA

6

Aa

9

aa

0

AA

.25

Aa

.50

aa

.25

AA

.4

Aa

.6

aa

0

How do you explain these data?


Hardy weinberg lab genetic drift

Hardy Weinberg Lab: Genetic Drift

Original population

Case #4 F5-1

6 individuals

12 alleles

p (A):0.5

q (a):0.5

total alleles = 12

p (A): (4+4+2)/12 = .83

q (a): (0+0+2)/12 = .17

AA

4

Aa

2

aa

0

AA

.25

Aa

.50

aa

.25

AA

.67

Aa

.33

aa

0

How do you explain these data?


Hardy weinberg lab genetic drift1

Hardy Weinberg Lab: Genetic Drift

Original population

Case #4 F5-2

5 individuals

10 alleles

p (A):0.5

q (a):0.5

total alleles = 10

p (A): (0+0+4)/10 = .4

q (a): (1+1+4)/10 = .6

AA

0

Aa

4

aa

1

AA

.25

Aa

.50

aa

.25

AA

0

Aa

.8

aa

.2

How do you explain these data?


Hardy weinberg lab genetic drift2

Hardy Weinberg Lab: Genetic Drift

Original population

Case #4 F5-3

5 individuals

10 alleles

p (A):0.5

q (a):0.5

total alleles = 10

p (A): (2+2+2)/10 = .6

q (a): (1+1+2)/10 = .4

AA

2

Aa

2

aa

1

AA

.25

Aa

.50

aa

.25

AA

.4

Aa

.4

aa

.2

How do you explain these data?


Hardy weinberg lab genetic drift3

Hardy Weinberg Lab: Genetic Drift

Original population

Case #4 F5

5 individuals

10 alleles

p (A):0.5

q (a):0.5

AAAaaapq

1.67.330.83.17

20.8.2.4.6

34.4.2.6.4

AA

.25

Aa

.50

aa

.25

How do you explain these data?


Measuring evolution of populations

Any Questions??


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