Outline of Last LectureOutline of Current LectureEvolution ReviewMechanisms of evolutionNatural SelectionSexual SelectionMale vs. Female“Social” mating systemsSummaryBio Sci 150 1st Edition Lecture 15Outline of Last Lecture 1. Evolution a. Key termsb. Evolutioni. Pattern and Processii. Misconceptionsc. Scientific Explanationsd. Evolution as a theoryi. Pattern of EvolutionOutline of Current Lecture 1. Evolution a. Review2. Natural Selectiona. Directional selection b. Stabilizing selection c. Disruptive/Diversifying selection d. Balancing selection 3. Sexual Selectiona. Male vs. Female****No class April 6th***Current LectureLECTURE QUESTION Natural selection…- Is a random process- Acts on populations to benefit the species- Act on individuals, and leads to evolution of populations - Mean s that only the strong surviveKey TermsNatural Selection - Differential survival and reproduction of genotypesThese 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.Directional selection - favors one extreme or the otherStabilizing selection - favors intermediate individuals Disruptive/Diversifying selection - favors different genotypes that produce different phenotypesBalancing selection - maintains genetic variation Sexual dimorphism - difference in appearance in males and femalesEvolution ReviewMechanisms of evolutionGenotype frequencies will not conform to H-W proportions if these mechanisms are operating:- Natural selection (non-random mating)- Mutation - Migration – moving and then reproducing - Genetic drift – random process; smaller population becomes weeded outNatural SelectionDefinition: Differential survival and reproduction of genotypes- Directional selection - favors one extreme or the othero Genetic variation is reduced - Stabilizing selection - favors intermediate individuals o Genetic variation is reduced - Disruptive/Diversifying selection - favors different genotypes that produce different phenotypeso Genetic variation is increased - Balancing selection - maintains genetic variation o Balanced polymorphism Two or more alleles are kept in balance, and therefore are maintained in a population over the course of many generationso 2 common ways Heterozygote Advantage- Increased variability is good!- Example: sickle-cell disease, mice (see power point) Negative frequency-dependent selection- Individuals with rare allele have higher fitness- Depends on context- Example: three-spine stickleback fish (see power point)Sexual SelectionDefinition: Occurs when individuals differ in their ability to attract mates. - A type of Natural Selection due to non-random mating- Helps to explain some of the most exaggerated traits in nature- Sexual selection often results in sexual dimorphismo Difference in appearance in males and femalesMale vs. Female- Sexual selection is usually stronger on males than females.- Females usually invest much more in their offspring than do males - The fundamental asymmetry of sex.o “Eggs are expensive and sperm are cheap” Eggs take more energy to produceo Leads to a fundamental difference in how each sex can increase their fitness  Female fitness is limited by the ability to produce eggs and rear young. Male fitness is limited by the ability to attract mates.o As a result: Females are more choosy about their mates - Females may also choose males that are more attractive Males compete more than females to acquire mates- Variation in reproductive success is greater for males than females. “Social” mating systems- Monogamous “one mate” 90% of bird species- Polygynous (5%) “many females”- Social relationships = paternity!o Extra-pair mating Species vary in the level of Extra-pair Paternity (mating outside monogamous pair-bonds) Extra-pair mating leads to high levels of variation in male reproductive success infairy-wrenstra-pairSummary1) Based on differential reproductive success=> males with the “best” traits produce the most young2) Explains traits that reduce