Transcript Document

Cavener & Clegg, 1981
Frequency of Recessive A lleles
0.6
0.5
Frequency (q)
0.4
w=0
w=0.25
w=0.5
0.3
0.2
0.1
0
0
1
2
3
4
5
Generations
6
7
8
9
10
Frequency of Recessive A lleles
1
0
1
2
3
4
5
6
7
8
9
10
0.1
Frequency (q)
0.01
0.001
w=0
w=0.25
w=0.5
0.0001
0.00001
0.000001
0.0000001
0.00000001
Generations
Elena/Lenski experiment
• Science, 1996
-Elena & Lenski, Science, 1996
Modes of Selection
Kuru - a prion disease
Pr
Pc
(normal)
(misfolded)
Kuru - a prion disease
Observed
Genotypic Freq. in
South Fore’
MM = 0.221
MV = 0.514
VV = 0.264
Obs. Genotypic Frq. in
South Fore’ Cannibals
MM = 0.133
MV = 0.767
VV = 0.1
• Hedrick, Science, 2003
Other overdominance
examples
•
•
•
•
Sickle cell anemia
Warfarin resistance in rats
Transferrin genotypes in pigeons
MHC class II
Modes of Selection
Modes of Selection
Campanula americana
(Tall Bellflower)
• Galloway & Etterson, J. Evol. Biol. 2003
Diopsids - Stalk-eyed Flies
(Cyrtodiopsis dalmanni)
•Wilkinson, Amitin & Johns
Integr. Comp. Biol., 2005
Negative Frequency-dependent Selection
Frequency of yellow morph
Aposematic
warning colors and markings
Mutation and Selection
Elena/Lenski experiment
• Science, 1996
-Elena & Lenski, Science, 1996
Migration & Drift
Water Snakes in Lake Erie
• Water snakes (Nerodia sipedon) in Lake
Erie come in two color phases: banded
and unbanded
• This is a two allele system
• Banded dominant to unbanded
• The mainland has really only banded
• The islands may have both
Lake Erie water snakes
• It was found that, when basking on islands,
the unbanded snakes are more cryptic and
thus remain hidden better.
• Why wouldn’t selection cause the unbanded
pattern to go to fixation?
• Migration. Every year, banded snakes
migrate from the mainland and introduce
fresh banded alleles
• Therefore, migration offsets selection
Genetic Drift