Chapter 16 Evolution of Populations

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Chapter 16 Evolution of Populations. Two main sources of genetic variation. Mutationschange in genes (DNA sequence) or chromosomes Gene recombinationmixing of genes that result from meiosis and sexual reproduction. - PowerPoint PPT Presentation


  • Chapter 16Evolution of Populations

  • Two main sources of genetic variationMutationschange in genes (DNA sequence) or chromosomesGene recombinationmixing of genes that result from meiosis and sexual reproduction

  • Gene Poolthe combined genetic information of all the members of a particular populaiton

  • Speciationformation of a new species through reproductive isolation Example: Galapagos Island finchesGround Squirrels

    **Quick Speciation Activity**

  • Fig. 24-6A. harrisiA. leucurus

  • Types of reproductive isolationBehavioral isolation (sympatric)Geographical isolation (allopatric)

    Which type did we demonstrate in our activity?

    If one of the Earths plates moves 1.9 cm a yr., in 1 million years it would move 12 miles

  • Geographic Isolation

    Some birds from species A cross to a second island.The two populations no longer share a gene pool.

  • Seed sizes on the second island favor birds with large beaks.The population on the second island evolves into population B, with larger beaks.Changes in the Gene Pool

  • Fig. 22-6(a) Cactus-eater(c) Seed-eater(b) Insect-eater

  • Speciesa group of similar organisms that can breed and produce fertile offspring

  • Fig. 24-2a(a) Similarity between different species

  • Exit Slip List the conditions required for a population to become a species.

  • Types of selection

  • 1. Disruptive Selection Selection that splits a population into 2 groups. Removes individuals with average traits, but keeps those with more extreme traits.

  • 2. Stabilizing SelectionEliminates extreme expressions of a trait when the average expression leads to higher fitness. Most common form of natural selection.

  • 3. Directional SelectionAn extreme version of a trait makes an organism more fit.

  • Height Selection Activity:Only extremely tall and extremely short Only mediumOnly extremely tall

  • 4. Sexual Selection Operates in populations where males and females look very differently.Typically, males will be larger and more colorful.

  • Types of Evolution

  • Adaptive radiation (divergent evolution) a single species evolves into several new species that live in different ways

  • Convergent evolutionunrelated species independently evolve similarities when adapting to similar environments

  • Coevolution two species evolve in response to changes in each other over time

    Example: mutualism

    Moth pollinates the comet orchid

  • Rate of Evolution

  • CatastrophismEvolution occurs after a catastrophy

  • GradualismEvolution proceeds in small, gradual steps

  • Punctuated Equilibrium Rapid spurts of genetic change that cause species to diverge quickly.These periods disrupt much longer periods when the species exhibit little change. Instances of abrupt transitions.

  • Chapter 17The History of Life

  • If one of the Earths plates moves 1.9 cm a yr., in 1 million years it would move 12 miles

  • Fossil recordinformation about past life that has been obtained from fossils-it is incomplete

  • Most organisms are now extinct2. fossils occur in a particular order3. groups of organisms have changed over time

  • Extincta species that has died out

  • Where do most fossils form?Most fossils form in sedimentary rock as weight compresses layers of sediment in bodies of water

  • Index Fossilan easily recognized species used to compare the relative ages of fossils

  • Sedimentary rocks form in horizontal layers.When part of Earths crust is compressed, a bend in a rock forms, tilting the rock layers.As the surface erodes due to water, wind, waves, or glaciers, the older rock surface is exposed.New sediment is then deposited above the exposed older rock surface.

  • Water carries small rock particles to lakes and seas.Dead organisms are buried by layers of sediment, which forms new rock.The preserved remains may later be discovered and studied.

  • Relative datingthe age of a fossil is determined by comparing its placement with fossils in other layersThe oldest layers are on the bottom

  • Half-lifethe length of time required for half of the radioactive atoms in a sample to decayCarbon-14 5770Uranium-235 713 million yrsPotassium-40 1.3 billion yrsUranium-238 4.5 billion yrs

  • Radioactive datingscientists use half-life to calculate the age of fossils based on the amount of remaining radioactive isotopes

  • Microfossilsmicroscopic fossil

  • Mass Extinctionmany types of living things become extinct in a short period of timeExample: Dinosaurs

  • ***