2Sickle-Cell AnemiaMutation + genetic variation + natural selection = evolution of a populationSickle- cell allele resulted from a single base mutation in the DNA coding for hemoglobinHeterozygous individuals, Ss, are resistant to malaria better chance of survivalSub-Sahara Africa- if you carry the allele, S, than you will survive to reproduce, and pass on the allele to the next generationTherefore, an increase in the frequency of the allele
4Directional Selection Occurs when selection favours an increase or decrease in the value of a trait from the current population average.Favours individuals with a more extreme variation of a traitResults in a shift away the average conditionRead Hummingbird example on the bottom of pg. 326
5Directional Selection Example -The soil in the original environment was a medium brown- After a volcano the soil becomes darkerMouse population evolved to blend in with the darker surroundingsTherefore, environment favoured individuals with more extreme variations of the trait
6Stabilizing Selection Selection against individuals exhibiting traits that deviate from the current populationThe average phenotype within a population is favoured by the environmentRead the human birth weight example on the bottom of page 327.
7Stabilizing Selection Example The soil remains medium brownMedium brown mice survive from predationMedium brown mice pass of their allele for medium brown fur to their offspringLight/ dark brown mice are eaten more -> those alleles are not passed on
8Disruptive SelectionSelection that favours two or more variations of a trait that differ from the current population average.Favours opposite extremes of a trait over individuals with intermediate variations
9Disruptive Selection Example Mouse move to a new environment with light brown rock and dark brown volcanic rockLight brown and dark brown mice blend in with their environment, but medium brown mice do notMedium brown mice are eaten by predatorsLight/ dark brown mice pass on their genes to future generations
10Hardy- Weinberg Equilibrium If allele frequencies change over time, the population is NOT in Hardy-Weinberg EquilibriumTherefore, a ‘disturbing factor’ is acting on the populationNatural SelectionSmall population sizeMutationImmigration/ EmigrationSexual selection