BIOLOGY 1M03 Lecture Notes - Lecture 6: Lazuli Bunting, Directional Selection, Endogamy
Document Summary
Directional selection: changes the average value of a trait, an extreme phenotype is favored by natural selection. Directional selection caused average size to increase in a cliff swallow population body size were able to survive the cold, but cannot fly as well. Stabilizing selection: reduces the amount of variation in a trait ex. Very small and very large babies are the most likely to die, leaving a narrower distribution of birth weights. Disruptive selection: maintains or increases the amount of variation in a trait, ex. Frequency dependant selection: negative frequency dependent selection- fitness is highest in rare phenotypes, ex. Snakes that have unique patterns are less likely to be eaten by birds: positive frequency dependent selection- fitness is highest in common phenotypes, ex. Frog bright color warns predators that they are toxic. Impact of selction on phenotypic variance and allelic diversity: different mechanisms can maintain/ increase or decrease phenotypic variance and diversity, but most decrease.
