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Transcript
Chapter 16 Population Genetics and Speciation Objectives CLE 3210.5.3 Explain how genetic variation in a population and changing environmental conditions are associated with adaptation and the emergence of new species. Darwin’s Finches http://people.rit.edu/rhrsbi/GalapagosPages/Pictures/LandBirds/FinchType http://www.biology-online.org/images/darwin_finches.jpg Five conditions under which evolution may take place Genetic mutations Gene flow Genetic drift Nonrandom mating Natural selection. Mutation Mutations are changes in the DNA. Gene Flow Emigration and immigration cause gene flow between populations and can thus affect gene frequencies. Genetic Drift Genetic drift is a change in allele frequencies due to random events. Genetic drift operates most strongly in small populations. Nonrandom Mating Mating is nonrandom whenever individuals may choose partners. Sexual selection occurs when certain traits increase an individual’s success at mating. Sexual selection explains the development of traits that improve reproductive success but that may harm the individual. Natural Selection Three general patterns Stabilizing Selection Disruptive Selection favors the formation of average traits. favors extreme traits rather than average traits. Directional Selection favors the formation of more-extreme traits. The Concept of Species Biological species concept a species is a population of organisms that can successfully interbreed but cannot breed with other groups Isolation and Speciation Geographic Isolation Allopatric Speciation Speciation due to separation of subgroups of a population Reproductive Isolation Results from the separation of population subgroups by geographic barriers. Results from the separation of population subgroups by barriers to successful breeding. Sympatric Speciation Reproductive isolation within the same geographic area Allopatry vs Sympatry http://deltabiology.com/wp-content/uploads/2012/02/Sympatry.jpg http://scienceblogs.com/evolvingthoughts/allopatry.jpg Reproductive isolation: Monkeyflower http://faculty.washington.edu/toby/images/mim29%20Nature.jpg Reproductive isolation http://evolution.berkeley.edu/evolibrary/images/evo/drosophila_scene7.g Rates of Speciation Gradualism species undergo small changes at a constant rate. Punctuated equilibrium new species arise abruptly, differ greatly from their ancestors, and then change little over long periods. Variation of Traits Within a Population Variations in genotype arise by mutation, recombination, and the random pairing of gametes. The Gene Pool The total genetic information available in a population is called the gene pool. Allele frequency is determined by dividing the total number of a certain allele by the total number of alleles of all types in the population Predicting Phenotype Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population. The Hardy-Weinberg Genetic Equilibrium Allele frequencies in the gene pool do not change unless acted upon by certain forces. Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable. Phenotype Frequency Calculating using the Hardy Weinberg equation Dominant allele frequency = p Recessive allele frequency = q p+q=1 p2 +2pq+ q2 = 1