Learning Objectives of populations 1 Describe how selection acting on individuals can result in evolution 2 Describe the sources of genetic variation in a population 3 Explain how examining the Hardy Weinberg equilibrium can tell us about evolution in a population 4 Describe how natural selection can function to drive evolution Chapter 21 Notes What is the difference between a species and a population Population is a group of species within a special area Gene Pool all alleles present in all individuals of a species Biological Evolution A change in the frequencies of the alleles in the gene pool Genetic Variation Some genetic variation is phenotypically detectable in easy to observe traits Some can only easily be detected at the level of molecules Mutations a new allele and the ultimate source of genetic variation Only germ line sex cells mutations can be passed on to the next generation Could be advantageous resulting in a better adapted Deleterious results in a less well adapted phenotype Neutral have no adaptive effect common phenotype rare common Recombination the reshuffling of mutations into new combinations Measuring Variations Observe traits first way to do it works well for traits Gel electrophoresis Can use blood or tissue samples controlled by one gene or not influenced by the environment to look for variation in proteins and you see the protein patterns DNA sequence variations DNA Sequencing Allows us to look directly at any Allele Frequencies of copies of an allele total of alleles in population Evolution A change in species or population over time A change in allele or genotype frequency in a Populations that are not evolving are in Hardy population over time Weinberg Equilibrium Hardy Weinberg Conditions All genotypes are equally well adapted no differences in the survival and reproductive success of individuals No gene flow populations must not be added to or subtracted from by migration No mutation no new alleles arising No genetic drift population must be sufficiently large to loss of allele by chance events Random Mating no mate preference The Hardy Weinberg relation describes the expected frequency of genotypes from allele frequencies p q 1 100 100 1 What force causes populations to evolve Darwin s Theory of Natural Selection surviving o It is not just random luck o Some individuals have a better chance at o More offspring produced than survive to o Inheritable variation among individuals of a o Best adapted individuals survive and adulthood overproduction reproduce Unequal reproductive Success species Adaptation Any characteristic that improves the survival or Organisms abilities to closely match the challenges Often is the result of natural selection reproductive success of an organism of their environment Fitness Contribution an individual makes to the gene pool of the next generation relative to the contributions of others offspring in the next generation Dominant male phenotype produces 300 male Small mae phenotype produce of 5 male offspring Female mimic phenotype produce 50 male offspring in the next genertion
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