Review of Natural Selection Types. Effects of Selection See Fig. 23.12 Coat color.
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Transcript of Review of Natural Selection Types. Effects of Selection See Fig. 23.12 Coat color.
![Page 1: Review of Natural Selection Types. Effects of Selection See Fig. 23.12 Coat color.](https://reader035.fdocuments.in/reader035/viewer/2022062517/56649e865503460f94b89214/html5/thumbnails/1.jpg)
Review of Review of Natural Natural
Selection TypesSelection Types
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Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
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Directional selection consistently favors phenotypes at one extreme
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Coat color
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Stabilizing selection favorsintermediate phenotypes
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Coat color
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Diversifying (disruptive) selection simultaneously favors both phenotypic extremes
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Coat color
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Effects of SelectionEffects of Selection
Directional, diversifying (disruptive), and stabilizing selection
See Fig. 23.12
Coat color
Coat color Coat color Coat color
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Population Population GeneticsGeneticsand the and the
Hardy-Weinberg Hardy-Weinberg EquationEquation
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Population GeneticsPopulation Genetics
• In the early 1900s these two men discovered how the frequency of a trait’s alleles in a population could be described mathematically.
G H Hardy – British Mathematician Wilhelm Weinberg – German Doctor
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Population GeneticsPopulation Genetics
• For every phenotype how many alleles do you have???– 2
• 1 from Mom and 1 from Dad
• These scientists figured out an equation that can be used to figure out the percentages of alleles and genotypes that are in a population.
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Population GeneticsPopulation Genetics
• In order for their equation to work the population has to be in genetic EQUILIBRIUM– There is no change in the gene pool =
no evolution
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Genetic EquilibriumGenetic Equilibrium• 1.) Population size is large• 2.) No gene flow in the population
• No new organisms introducing more alleles
• 3.) No mutations• 4.) No environmental factors causing
natural selection• No trait is favorable over another
• 5.) Random mating must occur
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The Hardy-Weinberg The Hardy-Weinberg EquationEquation
• p2 + 2pq + q2 = 1• p2 = frequency of the homozygous
dominant genotype• 2pq = frequency of the heterozygous
genotype• q2 = frequency of the homozygous
recessive genotype
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Hardy-WeinbergHardy-Weinberg• p – frequency of the dominant allele• q – frequency of the recessive allele• Because there are only 2 alleles, the
frequency of the dominant allele (p) and the frequency of the recessive allele (q) will add up to 1 or 100%
• p + q = 1
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Hardy-Weinberg ExampleHardy-Weinberg Example• In a population of 100 people 28 of them
were found to have freckles and 72 were not. We learned in class during our genetics unit that having freckles is a recessive trait and not having them is because of a dominant trait. If this population is in genetic equilibrium then solve for the allelic frequencies and the variables in the hardy-weinberg equation:
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Genetic DriftGenetic Drift
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Genetic DriftGenetic DriftGenetic Drift occurs when the frequency of alleles change due to RANDOM PROCESSES! (NOT natural selection)
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Bottleneck EffectBottleneck Effect
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Bottleneck EffectBottleneck Effect
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Founder EffectFounder Effect
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Queens full of Jacks!Queens full of Jacks!• Let’s Mate!• red card=dominant allele=R• black card=recessive allele=r
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P2 + 2pq + q2P2 + 2pq + q2RR Rr rr
Prediction 36% 48% 16%
1st gen.
2nd gen
3rd gen
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Predicted vs ActualPredicted vs Actual• If this population is in equilibrium, we
should have the predicted % for our genotypes…
• We have…20 rr envelopes and 30RR envelopes
• Are we in equilibrium?
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What should happen?What should happen?If we are evolving…If we are not…