review of natural selection types. effects of selection see fig. 23.12 coat color
TRANSCRIPT
Review of Review of Natural Natural
Selection TypesSelection Types
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Directional selection consistently favors phenotypes at one extreme
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Coat color
Stabilizing selection favorsintermediate phenotypes
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Coat color
Diversifying (disruptive) selection simultaneously favors both phenotypic extremes
Effects of SelectionEffects of Selection
See Fig. 23.12
Coat color
Coat color
Effects of SelectionEffects of Selection
Directional, diversifying (disruptive), and stabilizing selection
See Fig. 23.12
Coat color
Coat color Coat color Coat color
Population Population GeneticsGeneticsand the and the
Hardy-Weinberg Hardy-Weinberg EquationEquation
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
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.
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
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
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
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
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:
Genetic DriftGenetic Drift
Genetic DriftGenetic DriftGenetic Drift occurs when the frequency of alleles change due to RANDOM PROCESSES! (NOT natural selection)
Bottleneck EffectBottleneck Effect
Bottleneck EffectBottleneck Effect
Founder EffectFounder Effect
Queens full of Jacks!Queens full of Jacks!• Let’s Mate!• red card=dominant allele=R• black card=recessive allele=r
P2 + 2pq + q2P2 + 2pq + q2RR Rr rr
Prediction 36% 48% 16%
1st gen.
2nd gen
3rd gen
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?
What should happen?What should happen?If we are evolving…If we are not…