Biology 150: 2/1-2/3 Notes
Biology 150: 2/1-2/3 Notes Biology 150
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This 4 page Class Notes was uploaded by Shea Flannery on Sunday February 7, 2016. The Class Notes belongs to Biology 150 at University of Tennessee - Knoxville taught by Dr. Brian O'Meara in Spring 2016. Since its upload, it has received 107 views. For similar materials see Organismal and Ecological Biology in Biology at University of Tennessee - Knoxville.
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Date Created: 02/07/16
2/1 – Genes, Populations, and Species Hardy and Weinberg tested what would happen to the frequencies of alleles when many individuals in the same population mate and have offspring. Hardy and Weinberg wanted to know which genotypes would show up in the next generation and in what frequencies, so they calculated what would happen if two gametes were picked at random out of the gene pool several times, and were then combined to make offspring. A₁=p A₂=q p+q=1 (allele frequencies). Frequency of A₁A₁ is p². Frequency of A₂A₂ is q². Frequency of A₁A₂ is 2pq. Hardy-Weindberg equation: p²+2pq+q²=1 (genotype frequencies). When a random combination of gametes occur, the allele frequency does not change. The Hardy-Weinberg model is based on 5 assumptions about how populations and alleles behave: o Random mating o no natural selection o no genetic drift o no gene flow o no mutation Evolution will not occur if all 5 of the assumptions are met. The Hardy-Weinberg principle often acts as a null hypothesis when biologists want to test if one of the 5 assumptions is or is not occurring. 2/3 – Mechanisms of Evolution: Natural Selection Darwin and Wallace’s theory made two claims: o Species are related by common ancestry. o The characteristics of species can be modified from generation to generation-descent with modification. Natural selection occurs when: o Individuals in the same population vary in heritable characteristics. o In a specific environment, certain versions of the heritable traits help individuals survive better or reproduce more than other versions. Natural selection acts on individuals, but evolutionary change occurs in populations. All species are related by common ancestry and have changed over time because of natural selection. Typological thinking-species do not change and variations in species are unimportant. Aristotle organized the types of organisms into a linear scheme called the great chain of being or the scale of nature. Aristotle claimed that species are fixed types, and some species are higher (as in more complex or better) than others. Darwin is known for developing the idea of natural selection. Four postulates for evolution by natural selection: o Individual organisms that make up a population vary in the traits they possess. o Some of the trait differences are heritable. o In each generation, many more offspring are produces than can survive. o Individuals with certain heritable traits are more likely to survive and reproduce. The frequency of the heritable traits increases from one generation to the next. Natural selection causes a change in allele frequencies in a population over time. 4 postulates condensed: Evolution by natural selection occurs when heritable variation leads to differential reproductive success. The theory of evolution by natural selection is testable. Acclimation does not cause evolution. Mutations are random. Adaptations do not occur because organisms want or need them. Complex traits are often lost or simplified over time. There is no such thing as a higher or lower organism. Three other processes (genetic drift, gene flow, and mutation) change allele frequencies over time. Natural selection occurs in different patterns: o directional selection – reduces genetic variation. o stabilizing selection – reduces genetic variation. o disruptive selection – maintains genetic variation. o balancing selection – maintains genetic variation. Disruptive selection sometimes helps to create a new species. Heterozygote advantage maintains genetic variation. Natural selection increases fitness and leads to adaptation. Sexual selection usually acts on males more than females. Fundamental asymmetry of sex – females normally invest more in their offspring than males do. Females are limited by their ability to get the resources they need in order to produce more eggs and healthier young. Males are limited by the number of females they can mate with. Words to Know Acclimation Population Thinking Acclimatization Purifying Selection Adaptation Artificial Selection Balancing Selection Directional Selection Disruptive Selection Ecological (Environmental) Selection Evolution Fitness Fitness Trade-Off Frequency Gene Pool Genetic Correlation Genetic Variation Heritable Heterozygote Advantage Intersexual Selection Intrasexual Selection Natural Experiment Natural Selection Population Sexual Dimorphism Territory Stabilizing Selection Tuberculosis