Download - Measuring Evolution of Populations
![Page 1: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/1.jpg)
MeasuringEvolution of Populations
![Page 2: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/2.jpg)
Gene Variation is Raw MaterialEvolution - change over timeEvolution is descent with modification
DarwinThrough time, species accumulate differences such
that ancestral and descendent species are not identical.
![Page 3: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/3.jpg)
Gene Variation is Raw MaterialNatural selection and evolutionary change
Some individuals in a population possess certain inherited characteristics that play a role in producing more surviving offspring than individuals without those characteristics.The population gradually includes more individuals
with advantageous characteristics.
![Page 4: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/4.jpg)
Darwin versus Lamarck
![Page 5: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/5.jpg)
Macroevolution
It is large evolutionary change
Evolution of new species from a common ancestor
Evolution of one species into two or more species
![Page 6: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/6.jpg)
Microevolution Evolution on a small scale
Is the change in gene frequencies within a population over time
As the changes in populations accumulate, they can lead to the formation
of new species.
![Page 7: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/7.jpg)
Populations & gene poolsConcepts
a population is a localized group of interbreeding individuals
gene pool is collection of alleles in the populationremember difference between alleles & genes!
allele frequency is how common is that allele in the population how many A vs. a in whole population
![Page 8: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/8.jpg)
Hardy-Weinberg PrincipleHardy-Weinberg - original proportions of
genotypes in a population will remain constant from generation to generationSexual reproduction (meiosis and
fertilization) alone will not change allelic (genotypic) proportions.
![Page 9: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/9.jpg)
Hardy-Weinberg PrincipleNecessary assumptions
Allelic frequencies would remain constant if…population size is very largerandom matingno mutationno gene input from external sourcesno selection occurring
![Page 10: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/10.jpg)
Hardy-Weinberg theoremCounting Alleles
assume 2 alleles = B, bfrequency of dominant allele (B) = p frequency of recessive allele (b) = q
frequencies must add to 1 (100%), so:
p + q = 1
bbBbBB
![Page 11: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/11.jpg)
Hardy-Weinberg theoremCounting 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) =
2pqfrequencies of all individuals must add to 1 (100%), so:
p2 + 2pq + q2 = 1
bbBbBB
![Page 12: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/12.jpg)
H-W formulasAlleles: p + q = 1
Individuals: p2 + 2pq + q2 = 1
bbBbBB
BB
B b
Bb bb
![Page 13: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/13.jpg)
What are the genotype frequencies?What are the genotype frequencies?
Using Hardy-Weinberg equation
q2 (bb): 16/100 = .16
q (b): √.16 = 0.40.4
p (B): 1 - 0.4 = 0.60.6
q2 (bb): 16/100 = .16
q (b): √.16 = 0.40.4
p (B): 1 - 0.4 = 0.60.6
population: 100 cats84 black, 16 whiteHow many of each genotype?
population: 100 cats84 black, 16 whiteHow many of each genotype?
bbBbBB
p2=.36p2=.36 2pq=.482pq=.48 q2=.16q2=.16
Must assume population is in H-W equilibrium!Must assume population is in H-W equilibrium!
![Page 14: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/14.jpg)
Using Hardy-Weinberg equation
bbBbBB
p2=.36p2=.36 2pq=.482pq=.48 q2=.16q2=.16
Assuming H-W equilibriumAssuming H-W equilibrium
Sampled data Sampled data bbBbBB
p2=.74p2=.74 2pq=.102pq=.10 q2=.16q2=.16
How do you explain the data? How do you explain the data?
p2=.20p2=.20 2pq=.642pq=.64 q2=.16q2=.16
How do you explain the data? How do you explain the data?
Null hypothesis Null hypothesis
![Page 15: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/15.jpg)
Application of H-W principleSickle cell anemia
inherit a mutation in gene coding for hemoglobinoxygen-carrying blood proteinrecessive allele = HsHs
normal allele = Hb
low oxygen levels causes RBC to sicklebreakdown of RBCclogging small blood vesselsdamage to organs
often lethal
![Page 16: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/16.jpg)
Sickle cell frequencyHigh frequency of heterozygotes
1 in 5 in Central Africans = HbHs
unusual for allele with severe detrimental effects in homozygotes1 in 100 = HsHs
usually die before reproductive age
Why is the Hs allele maintained at such high levels in African populations?Why is the Hs allele maintained at such high levels in African populations?
Suggests some selective advantage of being heterozygous…Suggests some selective advantage of being heterozygous…
![Page 17: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/17.jpg)
Malaria Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells
Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells
1
2
3
![Page 18: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/18.jpg)
Heterozygote AdvantageIn tropical Africa, where malaria is common:
homozygous dominant (normal) die of malaria: HbHb
homozygous recessive die of sickle cell anemia: HsHs
heterozygote carriers are relatively free of both: HbHs
survive 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.
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
![Page 19: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/19.jpg)
Hardy-Weinberg equilibriumHypothetical, non-evolving population
preserves allele frequenciesServes as a model (null hypothesis)
natural populations rarely in H-W equilibriumuseful model to measure if forces are acting
on a populationmeasuring evolutionary change
W. Weinbergphysician
G.H. Hardymathematician
![Page 20: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/20.jpg)
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 change1. very large population size (no genetic drift)2. no migration (no gene flow in or out)3. no mutation (no genetic change)4. random mating (no sexual selection)5. no natural selection (everyone is equally fit)
http://nhscience.lonestar.edu/biol/hwe.html
![Page 21: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/21.jpg)
5 Agents of evolutionary changeMutation Gene Flow
Genetic Drift Selection
Non-random mating
![Page 22: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/22.jpg)
2005-2006
5 Agents of evolutionary change
![Page 23: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/23.jpg)
Five Agents of Evolutionary ChangeMutation
Mutation rates are generally so low they have little effect on Hardy-Weinberg proportions of common alleles.ultimate source of genetic variation
Gene flowmovement of alleles from one population to
anothertend to homogenize allele frequencies
![Page 24: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/24.jpg)
Five Agents of Evolutionary ChangeNonrandom mating
assortative mating - phenotypically similar individuals mateCauses frequencies of particular genotypes to differ
from those predicted by Hardy-Weinberg.
![Page 25: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/25.jpg)
Five Agents of Evolutionary Change
Genetic drift – statistical accidents.Frequencies of particular alleles may change by
chance alone.important in small populations
founder effect - few individuals found new population (small allelic pool)
bottleneck effect - drastic reduction in population, and gene pool size
![Page 26: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/26.jpg)
Genetic Drift - Bottleneck Effect
![Page 27: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/27.jpg)
Five Agents of Evolutionary Change
Selection – Only agent that produces adaptiveevolutionary changeartificial - breeders exert selection natural - nature exerts selection
variation must exist among individualsvariation must result in differences in numbers of viable
offspring producedvariation must be genetically inherited
natural selection is a process, and evolution is an outcome
![Page 28: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/28.jpg)
Five Agents of Evolutionary Change
Selection pressures:avoiding predatorsmatching climatic conditionpesticide resistance
![Page 29: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/29.jpg)
Measuring FitnessFitness is defined by evolutionary biologists
as the number of surviving offspring left in the next generation.relative measure
Selection favors phenotypes with the greatest fitness.
![Page 30: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/30.jpg)
Interactions Among Evolutionary ForcesLevels of variation retained in a population
may be determined by the relative strength of different evolutionary processes.
Gene flow versus natural selectionGene flow can be either a constructive or a
constraining force.Allelic frequencies reflect a balance between gene
flow and natural selection.
![Page 31: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/31.jpg)
Natural Selection Can Maintain Variation
Frequency-dependent selectionPhenotype fitness depends on its frequency within
the population.Negative frequency-dependent selection favors rare
phenotypes.Positive frequency-dependent selection eliminates variation.
Oscillating selectionSelection favors different phenotypes at different
times.
![Page 32: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/32.jpg)
Forms of SelectionDisruptive selection
Selection eliminates intermediate types.Directional selection
Selection eliminates one extreme from a phenotypic array.
Stabilizing selectionSelection acts to eliminate both
extremes from an array of phenotypes.
Sexual Selection
![Page 33: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/33.jpg)
Kinds of Selection
![Page 34: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/34.jpg)
Sexual selection Favours the selection of any trait
that confers an advantage in terms of the mating success of the individual
This is associated with sexual dimorphism: which is the physical (often extreme) differences in the appearance of males and females
The most common forms of sexual selection are the results of female mate choice and male to male competition
![Page 35: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/35.jpg)
Sexual selectionFemales can chose based on physical
traits, colouration, or behavioural traits such as courtship displays and songs
Sometimes males develop features that enable them to establish and defend a territory from other males=sometimes detaining the females
How would you be able to tell these are not env’tal selective pressures?
Both sexes would possess the features.
![Page 36: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/36.jpg)
Sexual selectionSome features are a compromise
between mating and remaining conspicuous to predators==bright colours and song.
![Page 37: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/37.jpg)
What about plants?Sexual diversity is not limited to just
animalsPlants do not select mates but they do
need to attract suitors to assist in pollination
Flowers and scents are the most obvious examples of sexual features that have evolved==maximize pollination
![Page 38: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/38.jpg)
Selection on Color in GuppiesGuppies are found in small northeastern
streams in South America and in nearby mountainous streams in Trinidad.Due to dispersal barriers, guppies can
be found in pools below waterfalls with high predation risk, or pools above waterfalls with low predation risk.
![Page 39: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/39.jpg)
Evolution of Coloration in Guppies
![Page 40: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/40.jpg)
Selection on Color in GuppiesHigh predation environment - Males
exhibit drab coloration and tend to be relatively small and reproduce at a younger age.
Low predation environment - Males display bright coloration, a larger number of spots, and tend to be more successful at defending territories.In the absence of predators, larger,
more colorful fish may produce more offspring.
![Page 41: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/41.jpg)
Evolutionary Change in Spot Number
![Page 42: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/42.jpg)
Limits to SelectionGenes have multiple effects
Pleiotropy - ex. PKUEvolution requires genetic variation
Intense selection may remove variation from a population at a rate greater than mutation can replenish.thoroughbred horses
Gene interactions affect allelic fitnessepistatic interactions –ex. You may have a
widows peak but if you have the baldness gene you will not see your widows peak.
![Page 43: Measuring Evolution of Populations](https://reader037.vdocuments.us/reader037/viewer/2022110101/56813260550346895d98f489/html5/thumbnails/43.jpg)
2005-2006
Any Questions??Any Questions??Any Questions??