Slide 1Fig. 15.1, p.453 Active Figure 15.1. Slide 2Fig. 15.2, p.455.
Evolution Mr. Wright, 2011. Sections 15.1 & 15.2.
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Transcript of Evolution Mr. Wright, 2011. Sections 15.1 & 15.2.
![Page 1: Evolution Mr. Wright, 2011. Sections 15.1 & 15.2.](https://reader036.fdocuments.in/reader036/viewer/2022062518/56649e795503460f94b788b7/html5/thumbnails/1.jpg)
EvolutionMr. Wright, 2011
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The Work of Charles DarwinSections 15.1 & 15.2
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Evolutionary Theory
•Evolution – change over time▫How modern organisms descended from their ancestors.
•Theory – a well-supported testable explanation for something
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Evolutionary Theory• The main person
behind evolutionary theory was Charles Darwin.
• Darwin sailed around the world, recording his observations as he travelled.
• These observations led to him proposing the idea of evolution.
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Darwin’s Observations
•Darwin was most influence by what he saw on the Galapagos Islands.
•Each island had a unique climate:▫Some were dry and barren▫Some were moist and diverse▫Others were inbetween
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Galapagos Tortoises
•Darwin found tortoises on each island, but they looked different from those on other islands.
•How are they different, and what might this mean?
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Galapagos Finches
•Darwin also studied finches on each island.
•How are they different? What might this mean?
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Adaptations
•An adaptation is any inherited characteristic that increases an organism’s chance of survival.
•These are key for outcompeting other organisms.
•Let’s look at a few examples and figure out what purpose they serve.
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Adaptation - Porcupine
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Adaptation - Hare
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Adaptation – Walking Stick
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Adaptation - Giraffe
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Adaptation - Whale
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Natural SelectionSection 15.3
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Variation is heritable.
•The variations that evolve over time can be passed on to offspring if an individual manages to reproduce.
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Artificial Selection
•Artificial Selection is when breeders select for certain desirable traits over time.
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The Struggle for Existence
•All organisms compete with each other to survive.
•Evolution selects for “better” organisms that have a greater chance at making it.
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Fitness
•Fitness – the ability of an organism to survive and reproduce in its environment
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Survival of the Fittest
•The organisms that are the most fit are the ones who survive. The weak will perish.
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Relation to Natural Selection
•Nature selects for the most fit individuals over time – only the fit live to reproduce and pass on their traits!
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Common Descent
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Homologous Structures
•Structures with different forms that develop from the same embryonic tissue.
•Typically, the more similar two structures are, the closer they are related.
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Embryology
•Embryos are very similar to one another from species to species – suggests a common ancestor?
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Darwin’s Theory - Summary
•Individuals differ, and variation is heritable.
•Organisms produce more offspring than will survive, and not all will reproduce.
•Organisms compete for limited resources.•Survival of the fittest!•All species share a common ancestor they
descended from.
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Genes and VariationSection 16.1
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Genes and Variation
•In the 1930’s, biologists began to connect Darwin and Mendel’s work to each other.
•Evolution is controlled by gene frequencies.
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Variation and Gene Pools
•Genetic variation is studied in whole populations.▫Population – group of individuals that can
interbreed.•Gene pool – ALL the different alleles that
occur in a population
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Variation and Gene Pools
•Relative Frequency – the number of times that an allele occurs in a gene pool compared to the total number of alleles
•Evolution is any change in the relative frequencies of alleles over time.
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Variation and Gene Pools•Relative Frequency
of the Green Allele = 12/15 = 4/5
•Relative Frequency of the Purple Allele = 2/15
•Relative Frequency of the Red Allele = 1/15
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Sources of Genetic Variation
•Mutations▫Changes to the genetic sequence of an
organism•“Gene Shuffling”
▫Remember that meiosis produces gametes that are all genetically unique
▫Produces many different combinations of alleles but DOES NOT change their relative frequencies in a population.
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Single-Gene Traits
•Variation for a trait can be caused by a single gene – you either have the trait, or you don’t.
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Polygenic Traits
•Many traits are controlled by several genes together – polygenic traits.
•Depending on how the genes combine, you can have several different phenotypes.
•Generally forms a bell-curve.
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Evolution as Genetic ChangeSection 16.2
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Review Concepts
•Fitness – an organism’s success at passing on its genes
•Adaptation – a genetically controlled trait that increases an individual’s fitness
•Natural selection determines what individuals survive and reproduces – an organism either passes on ALL genes, or none at all.
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Natural Selection on Single-Gene Traits•A forest lizard can appear in 3 colors:
brown, red (mutant), or black (mutant)
•What do you think might happen to the red allele over time?
•What do you think might happen to the black allele over time?
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Natural Selection on Single-Gene Traits•Due to natural selection, over time…
▫If an allele increases fitness, it’s relative frequency will increase.
▫If an allele decreases fitness, it’s relative frequency will decrease.
▫If an allele has no effect on fitness, it will not be affected by natural selection.
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Natural Selection on Polygenic Traits
•Remember that polygenic traits often form a bell curve.
•The fitness of individuals close to each other on the curve is similar, but can vary over great distances.
•Can be affected in three ways:
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Directional Selection
•When individuals at one sight of the curve are more fit than the other side, directional selection occurs.
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Stabilizing Selection
•When individuals at the center of the curve have the highest fitness stabilizing selection occurs.
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Disruptive Selection
•When the extremes have more fitness than the individuals in the middle, disruptive selection occurs.
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Genetic Drift
•Sometimes allele frequency changes simply due to chance – this is called genetic drift.
•Most common in small populations.
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Founder Effect
•Genetic drift can also occur when a small group goes off and colonizes a new habitat.
•This is known as the founder effect.
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The Hardy-Weinberg PrincipleSection 16.2
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Overview
•In order to study how evolution takes place, it can be useful to study a situation where NO CHANGE takes place.
•When allele frequencies remain constant it is called genetic equilibrium. No evolution occurs.
•This is called the Hardy-Weinberg Principle, and is made up of the following five rules.
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Random Mating
•All members of the population must have an equal opportunity to produce offspring.
•All alleles have an equal chance of being passed on.
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Large Population
•Genetic drift has less of an affect on a large population.
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No Immigration
•Immigrating individuals can either bring genes into or out of the population.
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No Mutations
•Mutations can affect the allele frequencies in a population.
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No Natural Selection
•All genotypes must have an equal chance of surviving and reproducing.
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The Process of SpeciationSection 16.3
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Speciation
•Speciation – the formation of a new species▫Species – group of organisms that can
breed and produce fertile offspring•Speciation is a product of evolution.•As species evolve, populations become
reproductively isolated and can no longer interbreed.
•3 ways that this can happen.
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Behavioral Isolation
•When two populations are capable of interbreeding but do not due to different reproductive behaviors.
•Example: Bird songs
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Geographic Isolation
•When a species is split into two new species by geological events it is geographic isolation
•Example: separation by mountains
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Temporal Isolation
•When two species do not reproduce due to time differences it is called temporal isolation.
•Example: rain forest orchids
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Example of Speciation - Assignment
•You will create a diagram showing the process of speciation in an organism of your choosing. The diagram should be at least 6 steps long.
•There is a good example of what I am looking for on pages 408-410 in your book.
•The book uses finches as their example – you must use something different. Tigers, turtles, dung beetles, aardvarks, whatever floats your boat.