SUMMARY OF LAST TIME

1
SUMMARY OFLAST TIME
Species influence each other's evolution Varies
from one species harming the other to both
benefiting (mutualism) Co-evolution often
diffuse can interact with more than one other
species Star orchids hawk-moths as example of
potential risks of over-specializing
2
QUICK ASSESSMENT
A is to the right as you look at this screen, Z
to the left Mark is given out of 15
3
QUICK ASSESSMENTS
Mean 50 (13 - 93)
4
1 11 21 31 41 51 61
71 81 91 10 20 30 40 50
60 70 80 90 100
5
MARKS IN CONTEXT
1
First
Honours
2i
2i
2ii
2ii
3
ordinary
Pass Ordinary
Fail
6
IDEAL TEST
Correct
Too easy
Guessing
7
THIS TEST
Correct
Too easy
Guessing
8
QUICK ASSESSMENT
Recycled questions this year 50 Mean for
same questions in past 64
9
WAS IT THE MATHS?
Maths 49 Other 50
10
I STILL WORRY ABOUT MATHS
No fewer than 14 of class got all four
numerical questions wrong If candidates did not
vary in maths ability you would expect this to be
only 4 (0.23 x 0.47 x 0.53 x 0.75)
11
WHICH QUESTIONS BOMBED?
this year
in past
12
WHICH QUESTIONS BOMBED?
this year
in past
13
THE GUILTY TRIO
Calculate allele frequency Principle of
segregation Point made with ß Globin Allele
K Selection acts against rare alleles that are
disadvantaged in heterozygote
14
TWO GUILTY MULTIPLE CHOICE
Both scored about 20, about the random
expectation So were you all guessing?
15
Mean mark for other questions
RIGHT
WRONG
16
LECTURE 11IMPERFECTION GUARANTEED
17
WILLIAM PALEY Divine Watchmaker
18
(No Transcript)
19
FIVE LIMITS TO ADAPTATION

• MUTATION VERY RARE

20
FIVE LIMITS TO ADAPTATION

• MUTATION VERY RARE
• GENETIC DRIFT CAN WIPE OUT ALLELES

21
RARE ALLELES ARE AT RISK
!?!
22
FIVE LIMITS TO ADAPTATION

• MUTATION VERY RARE
• GENETIC DRIFT CAN WIPE OUT ALLELES
• SELECTION OFTEN SLOW

23
(No Transcript)
24
MM Mt
tt Survival 34 34
17 Relative 1
1 0.5 Fitness
s 0.5
25
SELECTION FOR MELANIC
p
Start with p 0.001, s 0.5
years
26
gt 70 INDUSTRIAL MELANICS
Melanism e.g.
Peppered dominant
Moth Melanism
e.g. Scalloped recessive
Hazel
27
Industrial melanics usually involve dominant
alleles
28
SELECTION FOR MELANIC
p
dominant
Start with p 0.001, s 0.5
recessive
years
29
HARDY-WEINBERG RATIO
p2 2pq q2

30
RARE ALLELES ARE MAINLY IN HETEROZYGOTES
Proportion of alleles in heterozygote bodies
frequency of allele
31
SELECTION FOR MELANIC
p
dominant
Start with p 0.001, s 0.5
recessive
years
32
FIVE LIMITS TO ADAPTATION

• MUTATION VERY RARE
• GENETIC DRIFT CAN WIPE OUT ALLELES
• SELECTION OFTEN SLOW
• SELECTION OFTEN CONSTRAINED
• BY GENETICS (e.g. sickle cell)
  

33
GENETIC CONSTRAINTS

• S allele

AA AS SS
Mild Severe
anaemia anaemia
Moderate resistance to malaria
34
IF MALARIA PRESENT, RARE ALLELE SSPREADS LEADING
TO STABLE MIX
Start with q 0.001
STABLE q ? 0.11
0 Generations 50
35
STABLE MIX
Allele frequency of S, q ? 0.11 So, over 1 of
people condemned to death (q2 gt 0.01) IMPERFECT
ADAPTATION
36
GENETIC CONSTRAINTS

• K allele

AK SK KK
Extreme
anaemia
Moderate High
Resistance to malaria
37
EVEN IF MALARIA PRESENT, RARE ALLELE KCANNOT
SPREAD BY SELECTION
Start with q rising to 0.001
STABLE q 0.00
0 Generations 50
38
EVEN IF MALARIA PRESENT, RARE ALLELE KCANNOT
SPREAD BY SELECTION
Start with q rising to 0.001
STABLE q 0.00
0 Generations 50
39
NEW ALLELE K, 1 IN 1,000
0 Generations 20
40
ALLELE K CANNOT SPREAD BY SELECTION DESPITE K K
INDIVIDUALS BEING BEST ADAPTED
IMPERFECT ADAPTATION
41
ALLELE K CAN SPREAD BY CHANCE IN SMALL
POPULATIONS
42
ALLELE K UNLIKELY TO SPREAD FROM THESE SMALL
POPULATIONS
IMPERFECT ADAPTATION
43
KWELA
BANTU K only
A S
AK risk malaria SK extreme anaemia
44
FIVE LIMITS TO ADAPTATION

• MUTATION VERY RARE
• GENETIC DRIFT CAN WIPE OUT ALLELES
• SELECTION OFTEN SLOW
• SELECTION OFTEN CONSTRAINED
• BY GENETICS (e.g. sickle cell)
  
• BY ANCESTRY (e.g. Giant Panda)

45
GIANT PANDA Discovered in 1869
46
GIANT PANDA AN ENDANGERED BEAR
47
BAMBOO EATER
48
BAMBOO EATER
49
UNUSUAL FOR A BEAR
50
UNUSUAL FOR A BEAR
SAVE A SEAL EAT A VEGETARIAN
51
BEAR PAW
52
PANDAS THUMB
53
BAMBOO EATER
1 2 3 4 5
Radial Sesmoid
54
SEAL MURDERER
1 2 3 4 5
Radial Sesmoid
55
FIVE LIMITS TO ADAPTATION

• MUTATION VERY RARE
• GENETIC DRIFT CAN WIPE OUT ALLELES
• SELECTION OFTEN SLOW
• SELECTION OFTEN CONSTRAINED
• BY GENETICS (e.g. sickle cell)
  
• BY ANCESTRY (e.g. Giant Panda)
• GENE FLOW CAN COUNTER SELECTION

56
(No Transcript)
57
POLLUTION PLUME
Prevailing wind
TRANSECT
58
PEPPERED MOTH
melanics
Distance
59
SCALLOPED HAZEL (MOTH)
melanics
60
(No Transcript)
61
GENE FLOWLIZARD EXAMPLE
YY
YR
RR
INCOMPLETE DOMINANCE
62
ON YELLOW SOIL
1 s
1
1 - s
63
ON RED SOIL
1
1 s
1 - s
64
A PATCHYENVIRONMENT
65
CHARACTERISTIC LENGTH

• L d

s
d mean distance from birthplace to
breeding site
s selection coefficient
66
LOCALLY FAVOURABLE ALLELE SPREADS BY SELECTION
DESPITE GENE FLOW
IF PATCH MORE THAN 2L ACROSS

• IF PATCH MORE THAN 2L ACROSS

67
SMALL L(strong selectionor limited dispersal)
68
LARGE L(weak selectionor disperses widely)
69
MEDIUM L
70
A HABITAT BOUNDARY
TRANSECT
71
FREQUENCY OF RED ALLELE (p)
1.0
0.5
0
TRANSECT
72
WIDTH OF CLINE
p
0.75
0.25
TRANSECT
73
WIDTH 0.9 L
WIDTH OF A CLINE
p
0.75
0.25
TRANSECT
74
LOW L
HIGH L
TRANSECT