chapter 23 the evolution of populations. population genetics darwin and mendel –population...
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Chapter 23Chapter 23The Evolution of The Evolution of
PopulationsPopulations
Population GeneticsPopulation Genetics
Darwin and Mendel Darwin and Mendel – population geneticspopulation genetics
Gene pool and Allele frequency Gene pool and Allele frequency – fixed fixed – HeterozygousHeterozygous– Mind your p’s and q’s!Mind your p’s and q’s!
LE 23-4
Generation3 25% CRCR
Generation4
50% CRCW 25% CWCW
50% CW
gametes50% CR
come together at random
25% CRCR 50% CRCW 25% CWCW
Alleles segregate, and subsequentgenerations also have three typesof flowers in the same proportions
gametes
Generation2
Generation1
CRCR CWCW
genotypegenotypePlants mate
All CRCW
(all pink flowers)
50% CR 50% CW
gametes gametes
come together at random
X
Calculate allele frequencies:
500 total flowers
320 red
160 pink
20 white
Freq CR:
FreqCW:
The Hardy-Weinberg TheoremThe Hardy-Weinberg Theorem
Allele frequencies in a population Allele frequencies in a population remain unchangedremain unchanged– Basis for understanding long-term Basis for understanding long-term
evolutionary changesevolutionary changes H-W equilibrium – pH-W equilibrium – p22 + 2pq + q + 2pq + q22 = 1 = 1
– p + q = 1p + q = 1
LE 23-5Gametes for each generation are
drawn at random from the gene poolof the previous generation:
80% CR (p = 0.8) 20% CW (q = 0.2)
SpermCR
(80%)CW
(20%)
pqp2
16%CRCW
64%CRCR
Eg
gs
CW
(20%
)C
R
(80%
)
16%CRCW
qp4%
CWCW
q2
Conditions for Hardy-WeinbergConditions for Hardy-Weinberg
Large population sizeLarge population size No gene flowNo gene flow No mutationsNo mutations Random matingRandom mating No natural selectionNo natural selection
Sources of VariationSources of Variation
MutationsMutations– Point mutationPoint mutation– Alter gene number or sequenceAlter gene number or sequence
duplicationduplication
– Mutation ratesMutation rates Sexual recombinationSexual recombination
Altering Populations Gene Pool: Altering Populations Gene Pool: The Big PlayersThe Big Players
Natural selectionNatural selection Genetic DriftGenetic Drift
– Bottleneck effectBottleneck effect– Founder effectFounder effect
Gene flowGene flow
LE 23-7
CRCR CRCR CWCW CRCR
CRCW
CRCR
CRCW
CWCW
CWCW
CRCW CRCW
CRCRCRCW
CRCWCRCR
CRCR
CRCW
CWCW
CRCW
CRCR
Only 5 of10 plantsleaveoffspring
Only 2 of10 plantsleaveoffspring
CRCR
CRCR
CRCR CRCR
CRCR
CRCR CRCR
CRCR
CRCR
CRCR
Generation 2p = 0.5q = 0.5
Generation 3p = 1.0q = 0.0
Generation 1p (frequency of CR) = 0.7q (frequency of CW) = 0.3
LE 23-8
Originalpopulation
Bottleneckingevent
Survivingpopulation
Natural Selection and Adaptive Natural Selection and Adaptive EvolutionEvolution
Genetic variationGenetic variation– PolymorphismPolymorphism– Geographic variationGeographic variation
Closer look at Natural SelectionCloser look at Natural Selection– Evolutionary fitnessEvolutionary fitness– Types of selectionTypes of selection
Preservation of genetic variationPreservation of genetic variation Sexual SelectionSexual Selection
LE 23-10
1 2.4 3.14 5.18 6 7.15
8.11 9.12 10.16 13.17 19 XX
1
9.10 11.12 13.17 15.18 XX
2.19 3.8 4.16 5.14 6.7
LE 23-11Heights of yarrow plants grown in common garden
Sierra NevadaRange
Great BasinPlateau
Seed collection sites
100
50
0
3,000
2,000
1,000
0
Mea
n h
eig
ht
(cm
)A
lti t
ud
e (m
)
LE 23-12a
Original population
Phenotypes (fur color)
Fre
qu
ency
of
ind
ivid
ual
s
LE 23-12b
Originalpopulation
Evolvedpopulation
Directional selection Disruptive selection Stabilizing selection
LE 23-13
Frequencies of thesickle-cell allele
0–2.5%
2.5–5.0%
5.0–7.5%
7.5–10.0%
10.0–12.5%
>12.5%
Distribution ofmalaria caused byPlasmodium falciparum(a protozoan)
LE 23-14
Parental population sample
Experimental group sample
On pecking a mothimage the blue jayreceives a food reward.If the bird does notdetect a moth oneither screen, it pecksthe green circle tocontinue a new setof images (a newfeeding opportunity).
Plain background Patterned background
0.6
0.5
0.4
0.3
0.2
0 20 40 60 80 100
Generation number
Frequency-independent control
Ph
eno
typ
icva
riat
ion