Genetic Variation I Evolution as Genetic Change Evolution

Genetic Variation I. Evolution as Genetic Change B. Sources of Variation: 1. Mutations: Change

Natural Selection II. Distribution of Phenotypes Evolution is a change over time. So, how

1. Directional selection: Individuals at one end of the curve have a higher fitness

2. Stabilizing Selection: Individuals near the center of the curve have higher fitness than

3. Disruptive selection: Individuals at either end of the curve have higher fitness than

Evolution in Process III. Evolution Changes in a population, over time, in response to

Evolution in Process C. Divergent Evolution: Previously related organisms become less alike. Two types:

INSECTS CRACKING SEEDS What food source are these beak shapes most likely adapted for?

Evolution in Process V. Mechanisms for Evolution, or change in a population, occurs at

Evolution in Process V. Mechanisms for Evolution B. Migration: Changes occur as individuals move

Evolution in Process V. Mechanisms for Evolution C. Isolation: Separation of populations into groups

3. Temporal Isolation: Reproduction occurs at different times the Ex: Frogs: one species mates

V. Mechanisms for Evolution D. Punctuated Equilibrium: Long stable periods of populations interrupted by

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Genetic Variation I. Evolution as Genetic Change Evolution is dependent upon genetic variation within a population. A. Background Information: 1. Gene Pool: Consists of all genes, including all the different types of alleles, that are present within a population. 2. Relative Frequency: number of times that a particular allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur.

Genetic Variation I. Evolution as Genetic Change B. Sources of Variation: 1. Mutations: Change in the DNA sequence. Some can affect an organisms fitness or ability to survive and others have no effect. 2. Gene Shuffling: During Meiosis crossing over occurs and mixes up the alleles. You don’t look exactly like your siblings, different alleles were passed on to each of you.

Natural Selection II. Distribution of Phenotypes Evolution is a change over time. So, how does a population change over time in relation to their gene pool. A. 3 ways in which natural selection can affect the distribution of phenotypes: 1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection

1. Directional selection: Individuals at one end of the curve have a higher fitness than individuals in the middle or at the other end of the curve. Ex: Birds with larger beaks are more successful than those with medium or small sized beak due to some change in the environment.

2. Stabilizing Selection: Individuals near the center of the curve have higher fitness than individuals at either end of the curve. Ex: Human babies tend to be fairly close in weight. Being born too small or too large was selected against. Therefore the curve moves towards the middle.

3. Disruptive selection: Individuals at either end of the curve have higher fitness than those in the middle. Ex: Bird with smaller and larger beaks are more successful than those with medium sized beaks. Due to some change in the environment. THIS LEADS TO NEW SPECIES!

Evolution in Process III. Evolution Changes in a population, over time, in response to environmental pressures. IV. Patterns of Evolution A. Coevolution: Evolution of two species that interact together. Ex: A prey changes, so the predator must also change. (Knute and Snake!) B. Convergent Evolution: Unrelated organisms develop similar characteristics due to similar environments. (Ex: dolphins and sharks)

Evolution in Process C. Divergent Evolution: Previously related organisms become less alike. Two types: 1. Adaptive Radiation Many related species evolve from a single ancestral species Ex: Different beak shapes for different food sources

INSECTS CRACKING SEEDS What food source are these beak shapes most likely adapted for?

Evolution in Process V. Mechanisms for Evolution, or change in a population, occurs at irregular rates throughout history (punctuated equillibrium). What causes these changes? A. Background Information: 1. Species: A population of interbreeding organisms capable of producing fertile offspring. 2. Speciation: Formation of a new species.

Evolution in Process V. Mechanisms for Evolution B. Migration: Changes occur as individuals move into or out of a population. 1. Immigration: Movement into a population 2. Emigration: Movement out of a population

Evolution in Process V. Mechanisms for Evolution C. Isolation: Separation of populations into groups that no longer interact. 1. Geographic Isolation: Physical separation Ex: Squirrels on either side of the Grand Canyon 2. Genetic/Reproductive Isolation: Inability for populations to interbreed Ex: A horse and a donkey can produce a mule, but that mule cannot reproduce

3. Temporal Isolation: Reproduction occurs at different times the Ex: Frogs: one species mates during day and the other at night 4. Behavioral Isolation: Different courtship rituals or reproductive strategies Ex: Eastern and Western Meadowlarks have different songs to attract mates

V. Mechanisms for Evolution D. Punctuated Equilibrium: Long stable periods of populations interrupted by brief periods of more rapid change. 1. Gradual change: Fossil records confirm that generally populations change very slowly over time. Ex: Many fish fossils show slow changes. 2. Rapid Change: Something happens to a populations equilibrium to cause sudden changes in the gene pool. Ex: Geographic Isolation of two groups within a population. Migration and Immigration.