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One area lacking in Darwin’s analysis

 _{1) Competition creating selective force}

 _{2) Variety of heritable traits}

 _{3) Selection of organisms to out-reproduce}

others

 _{4) Generations of over-reproduction to foster}

population change

How is this variety

Modern evolutionary theory

 _{Darwinian evolution + genetic analysis = modern}

synthesis

 _{Methodology: analyze a population’s gene pool, see if}

its allele frequencies are changing over time

 _{Population – all organisms of same species in an area}

 _{Gene pool – all of the genes of population considered}

together

 _{Allele frequency – percentage of a specific allele}

Example of gene pool

 _{Studying a population of rock pocket mice}

 _{Sandy-fur mice = RR (25 organisms)}  _{Sandy-fur mice = Rr (17 organisms)}  _{Black-fur mice = rr (3 organisms)}

 _{Total alleles = 25 x 2 + 17 x 2 + 3 x 2 = 90}

 _{R allele frequency = 25 x 2 + 17 x 1 = 67 / 90 =}

74.4%

Allele frequencies and evolution

 _{Update definition of evolution as change in}

allele frequencies over generations

 _{Ex: Lava flow creates black rock environment}

Genotypes # organisms initially

# organisms

25 years later

RR

25

2

Rr

17

4

Calculate new allele frequency

 _{Initially: R = 74.4% r = 25.6%}

Genotypes # organisms initially

# organisms

25 years later

RR

25

2

Rr

17

4

rr

3

41

 _{25 years later: Total alleles = (2 + 4 + 41) x 2}

= 94

 _{R = 2 x 2 + 4 x 1 = 8 / 94 = 8.5%}

So what causes evolution?

 _{More than just natural selection}

 _{First, let’s discuss when no change occurs =}

Hardy – Weinberg equilibrium

 _{Hardy and Weinberg create mathematical}

Hardy – Weinberg equilibrium

constant if:

1.No gene flow (emigration or immigration)

2.No mutations occur

3.No natural selection is occurring

4.Population is large in number (infinitely large)

Hardy – Weinberg equilibrium

 _{If 5 assumptions met, no evolution occurs}

 _{This also means that sexual reproduction itself}

does NOT change population allele frequencies

 _{Sexual reproduction does create genetic variety}

in individuals BUT NOT in population

So what causes evolution?

 _{Let’s break the 5 assumptions one at a time}

1.No gene flow (emigration or immigration)

2.No mutations occur

3.No natural selection is occurring

4.Population is large in number (infinitely large)

Evolutionary force #1: gene flow

 _{Entry of new individuals or exit of current}

members

 _{Initially: R = 74.4% r = 25.6%}

Genotypes # mice in desert

# mice + 10 new black

fur mice

RR

25

25

Rr

17

17

rr

3

13

 _{After gene flow: R = 60.9% r = 39.1%}

So what causes evolution?

 _{Let’s break the 5 assumptions one at a time}

1.No gene flow (emigration or immigration)

2.No mutations occur

3.No natural selection is occurring

4.Population is large in number (infinitely large)

Evolutionary force #2: mutation

 _{Causes very little change by itself}

 _{Example: new mutation at another gene locus}

causes albino coloration in just one mouse

(updating Darwin)

Genotypes # organisms initially

# organisms

after mutation

event

AA

0

0

Aa

0

1

aa

45

47

Before:

A = 0%

a =

100%

After:

A = 1%

So what causes evolution?

 _{Let’s break the 5 assumptions one at a time}

1.No gene flow (emigration or immigration)

2.No mutations occur

3.No natural selection is occurring

4.Population is large in number (infinitely large)

Evolutionary force #3 – natural selection

 _{The example we discussed before (mice}

invading black volcanic rock territory)

Genotypes # organisms initially

# organisms

25 years later

RR

25

2

Rr

17

4

rr

3

41

(Darwin’s idea)

Before:

R = 74.4%

r = 25.6%

After:

Real life examples

 _{1) Stabilizing selection – child birth weight}

 _{2) Directional selection – anteater snout}

length

 _{3) Disruptive selection – limpet shell}

So what causes evolution?

 _{Let’s break the 5 assumptions one at a time}

1.No gene flow (emigration or immigration)

2.No mutations occur

3.No natural selection is occurring

4.Population is large in number (infinitely large)

Evolutionary force #4: Genetic drift

 _{Before, we said sexual reproduction does}

NOT change overall gene pool

 _{This assumes a large population where actual}

results more likely match predictions

R

R

r

r

RR

Rr

Rr

rr

Evolutionary force #4: Genetic drift

randomly

 _{Could be randomness of sexual reproduction, or any}

other random event (natural disaster)

 _{Smaller populations have larger changes potentially}

Frequencies:

Before: R = 50%, r = 50% After: R = 23%, r = 77%

Genotype s # mice in desert # mice after

RR

0

0

Rr

4

7

Evolutionary force #4: Genetic drift

 _{Bottleneck effect – natural disaster kills many}

organisms, survivors

 _{Founder effect – very small population}

isolated from larger population in new area (ex: islands)

 _{Genetic drift tends to reduce variety}

So what causes evolution?

 _{Let’s break the 5 assumptions one at a time}

1.No gene flow (emigration or immigration)

2.No mutations occur

3.No natural selection is occurring

4.Population is large in number (infinitely large)

Evolutionary force #5: Sexual selection

 _{Mate choice for particular characteristics}

makes certain traits more prominent

 _{Tends to be female choice of males in many}

species

Evolutionary force #5: Sexual selection

S = sexy phenotype s = not so sexy

Genotypes # organisms before

# organisms after 10 generations

SS

3

14

Ss

10

12

ss

17

4

Before:

S = 26.7%

s = 73.3%

After:

Overall summary

equilibrium

1) No gene flow (no

immigration / emigration) 2) No mutation

3) No natural selection 4) Infinitely large

population

5) Random mating

 _{Evolutionary forces}

1) Gene flow

2) Mutation

3) Natural selection 4) Genetic drift

Hardy-Weinberg equations

 _{IF H-W equilibrium exists, we can calculate}

allele frequencies and genotype frequencies in population if we know one component

 _{Calculations always involve decimals, not}

percentages

40% = 0.40 6.3% = 0.063

 _{Equation #1:}

p + q = 1 p = overall dominant allele % in gene pool q = overall recessive allele % in gene pool

Hardy-Weinberg equations

(2 homologous chromosomes)

(p + q) x (p + q) = 1 p = dominant allele q = recessive allele

 _{Equation #2:}

p2 + 2pq + q2 = 1

Gene pool idea

R = black

fur

r = sandy

fur

RR

Rr

Rr

Rr

rr

rr

rr

rr

rr

rr

rr

rr

rr

rr

rr

rr

rr

Rr

Rr

rr

(20 total

organisms)

14 / 20 = rr =

70%

7 / 40 R =

17.5%

1 / 20 = RR =

5%

5 / 20 = Rr =

25%

33 / 40 r =

82.5%

or p = 0.175

or q = 0.825

or p

~

0.05

or 2pq ~

0.25

or q

~

0.70

Gene pool

Hardy-Weinberg calculations

solve for other parts

 _{Often, this component is the recessive phenotype –}

q2

 _{Ex: If 1 in 30,000 Americans has cystic fibrosis}

(assume ~ 300,000,000 Americans), how many

Americans are carriers, assuming H-W equilibrium?

Cystic fibrosis H-W problem

 _{Given q}2, we can find q = √ q2

 _{Then we can find p: p + q = 1}

so p = 1 –q = 1 - √ q2

 _{Then 2pq = 2(1 - √ q}2) √ q2

 _{2pq = 2 (1 – √0.00003)(√ 0.00003) = 0.0115}

= 1.15%

 _{1.15% of 300,000,000 Americans ~ 3,444,100}

Cystic fibrosis H-W problem

 _{Then we can find p: p + q = 1}

so p = 1 –q = 1 - √ q2

 _{Then 2pq = 2(1 - √ q}2) √ q2

 _{2pq = 2 (1 – √0.00003)(√ 0.00003) = 0.0115 =}

1.15%

 _{1.15% of 300,000,000 Americans ~ 3,444,100}

Solving without a calculator

 _{Can you do these calculations?}

2 x 0.60 x 0.40 = (0.30)2 =

(0.60)2 = √(0.04) =

Final reminder

 _{These calculations assume population is in}

H-W equilibrium