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Evolution I & II – Natural selection, Other mechanisms

by: KyCa

Evolution I & II – Natural selection, Other mechanisms ECOL 182R

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Lectures 2 & 3 – Spring 2016, ECOL 182R - Hunter, Bonine. Evolution I & II – Natural selection, Other mechanisms
Introductory Biology II
Bonine, Hunter, Martinez
Class Notes
ECOL 182R 182 Hunter Arizona Bonine 2016
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This 2 page Class Notes was uploaded by KyCa on Sunday February 28, 2016. The Class Notes belongs to ECOL 182R at University of Arizona taught by Bonine, Hunter, Martinez in Spring2015. Since its upload, it has received 56 views. For similar materials see Introductory Biology II in Science at University of Arizona.


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Date Created: 02/28/16
Lecture 2 – Evolution 1: Natural Selection Aristotle (384-322 BC): “Scala naturae” = “great chain of being”, ranks organisms along continuum by ‘perfection’; progressive chain of being ranks organisms by “progress” towards a point. Linnaeus, Carolus (1707-1778): Father of taxonomy; binomial nomenclature; hierarchal classification (Domain … DKPCOFGS) based on similarities/differences. Charles Darwin (1809-1882): Evolution by natural selection; 5 years on HMS Beagle – notes on new pigeon breeds from trip were used to form his theory. Phylogeny: the evolutionary history of an organism. Phylogenic tree: depicts organisms’ phylogenies and their evolutionary relationships; shows relatives and ancestors. - Root: represents the common ancestor of all species o n tree. - Branch: represents a lineage through time. - Node: represents a speciation event and the common ancestor at time of split. - Clade: a common ancestor and all of its descendants (also, monophyletic group). o Can be cut off from rest of tree with a single snip. Monophyletic group: (clade) includes the common ancestor and ALL of its descendants. Paraphyletic group: includes common ancestor and only SOME of its descendants (not all). Polyphyletic group: composed of a group of organisms, NOT including their common ancestor. Crypsis: camouflage obtained through matching one’s body coloration with their background. Adaptions: inherited traits favored by natural selection. Agent of selection: a factor that selects for one variation over another; can include pr edators, weather, food quality, pathogens, moisture, etc. Inherited Traits upon which selection can act: - Discrete Traits: traits with few possible phenotypes that fall into distinct classes; controlled by only 1-2 genes and one form of the gene (allele) i s dominant. Ex: brown/blue/green (eye color), brown/white (lizards), wrinkled/smooth (peas). - Continuous/Quantitative traits: traits that show continuous variation across a population and are not grouped into discrete categories; controlled by many genes wi th smaller impacts. Offspring is usually an intermediate between parents. Ex: height, weight, blood pressure. o Normal distribution (bell curve) when graphed. Natural Selection on normally-distributed (quantitative) traits : - Directional selection: individuals on one end of distribution do best. - Stabilizing selection: average individuals do best. - Disruptive selection: individuals on both ends of distribution do best (average do worst). Lecture 3 – Evolution 2 Evolution: the change in allele frequencies in a population of organisms over time. Population: a potentially interbreeding individuals of the same species. Allele: one version of a gene. Allele frequency: frequency of an allele within a population. Allele fixation: an increase in an allele frequency to 100%, until only one allele remains. Population bottleneck: a sharp reduction in population size within a short time period, often resulting in significant changes in allele frequencies and variation, in dependent of selection; reduces variation in the gene pool. Genetic drift: the random shift in allele frequencies f rom one generation to the next; reduces genetic variation within populations (esp. small populations) and can even lead to allele fixation. Does not make populations better adapted t o environment. Gene flow: the movement of alleles from one population to another, generally as a result of individual migration/immigration/etc.; reduces the local effects of natural selection and halts speciation. Mutation: a nucleotide change in one’s genetic code, sometimes giving rise to a new allele; source of all genetic variation; can involve deletions (most common), insertions, or substitutions (point mutations, 1 nucleotide change). Rare per gene, common per genome , but rarely generate completely new traits – just change existing ones. Germ cell mutations are ultimately the source of almost all genetic variation . Mutagen: an agent that causes a genetic mutation. Germ cell: haploid cells the give rise to gametes (reproductive cells) within sexually-reproducing organisms; contains the genetic material that is passed down between generations; source of almost all genetic variation. Natural Selection R equirements: - Variation: trait must vary among individuals within a population - Heritability: trait must be heritable - Fitness advantage: trait must confer a fitness advantage; more individuals with the trait survive and reproduce than those without it. o Agent of selection is responsible for differential fitness levels of individuals. 4 Mechanisms of Evolution: - natural selection - genetic drift (reduces genetic variation) - gene flow (counters effects of natural selection) - mutation (increases genetic variation) Reduced genetic variation poses a threat to populations because populations are less able to adapt to environmental changes –– can even lead to extinction. Human Influenced Selection (examples): 1. Industrial melanism in pepper moths, 2. Resistance to antibiotics in bacteria, 3. Resistance to herbicides by weedy plants, 4. Resistance to pesticides by insects, 5. Reduction in fish size due to gill nets.


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