BIO 171 1st Edition Lecture 9Outline of Last Lecture I. Complex traitsII. Evolution by Natural SelectionOutline of Current Lecture I. Types of Selection Cont. II. Sexual Selection III. Genetic Drift/Gene Flow Current LectureTypes of Selection Cont. -Directional Selection- One tail of phenotypic distribution is favored (or 1 allele)oThe population mean changes oGenetic variation is reduced because some alleles are lost, while others are fixed -Stabilizing Selection- Individuals with intermediate phenotypes have highest fitness (extremes have low fitness)oThe population mean for the trait stays the same oGenetic variation is reduced because alleles that produce extreme phenotypes are lost -Disruptive Selection- Intermediate phenotypes are selected against and extreme phenotypes have the highest fitness oThe population mean does not change significantly oGenetic variation is maintained or increased Sexual Selection -Sexual selection promotes traits that increase an individual's access to reproductive opportunities These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.oIndividuals that posses certain heritable traits are more successful at attracting and obtaining mates and thus reproduce at a higher rate relative to other individuals in the population.oThese traits sometimes appear to run counter to those favored by natural selection -Sexes often differ in morphology, behavior, and physiology (more prominent in males)oMorphology: Males can be larger, brighter in color, posses some extra feature, etc. oBehavior: Males can express a certain call, act, behavior, etc. to catch female's attention oPhysiology: differences in hormones and/or brain structure -Males compete more intensely for mates than females, while females are choosier about their mates than malesoAnisogamy- gametes of different sizes -Males have many small gametes (sperm)-Females have few larger gametes (eggs)oFemales are choosier with their mates because they invest more per egg -Forms of sexual selection: oIntrasexual Selection- competition within a sex (most commonly seen in males) for access to the other sex- selects for male traits oIntersexual Selection- selection between the sexes (female mate choice)- selects for male traits oBoth forms can lead to sexual dimorphism -Sexual Dimorphism- differences between the sexes in traits often related to attracting and obtaining mates Genetic Drift/ Gene Flow -Genetic drift is the random change in allele frequencies from generation to generation oGenetic drift is less extreme in large populations and more extreme in small populations -Ways to get small populations that are heavily affected by genetic drift: Founder Effect- loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population Genetic Bottleneck- a sharp reduction in the size of population (and genetic variation) due to environmental events, or human activitiesIn both, the new population is likely to have different allele frequencies than the source population, by chance-Gene flow is the movement of alleles from one population to another oGene flow between populations makes connected populations have more similarallele frequencies oIt can increase or decrease genetic variationoGene flow between populations can counteract the effects of selection or geneticdrift by introducing new alleles to the