Hardy-Weinberg Equilibrium -And how it affects evolution.

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Hardy-Weinberg Equilibrium -And how it affects evolution.

Transcript of Hardy-Weinberg Equilibrium -And how it affects evolution.

Page 1: Hardy-Weinberg Equilibrium -And how it affects evolution.

Hardy-Weinberg Equilibrium

-And how it affects evolution.

Page 2: Hardy-Weinberg Equilibrium -And how it affects evolution.

Hardy-Weinberg Principle• Predicts how gene frequencies

(number of dominant and recessive alleles) will be transmitted from generation to generation.

• The genes of a population are known as the gene pool.

• The Hardy-Weinberg principle states that there will be no change in allele frequency of a population over time. This is called genetic equilibrium.

Page 3: Hardy-Weinberg Equilibrium -And how it affects evolution.

Hardy-Weinberg Equilibrium

• Genetic equilibrium will not change over time-

• Frequencies in each successive generation will be the same as the original parent generation.

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Hardy-Weinberg Equilibrium

• There are five conditions that must be met for Hardy Weinberg Equilibrium to occur in a population (no changes in allele frequencies):– large population– random mating – no mutations– no gene flow– no selection

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Large Population

• A large population is less likely to have random fluctuations change allele frequencies than smaller populations.

• Small populations are more likely to experience genetic drift- change in allele frequency by chance– Think of a coin toss. The more you

toss the coin, the greater your chances of flipping 50% heads and 50% tails.

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Random Mating

• Individuals must randomly mate with other individuals within a population.

• Non-random mating will result in changes in allele frequency.

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Non-Random Mating

• Types of non-random mating:– Assortative mating- choosing

mates with similar phenotypes

– Competition- some males compete for mates

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Mutations

• Mutations- Spontaneous changes in an allele.

• Increase variation in a population when old alleles change into new alleles.

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Gene Flow

• Gene flow- caused by migration.

• New alleles are introduced into a population when new individuals move in.

• Alleles are removed from the population when individuals move out of a population.

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Selection

• Natural selection tends to reduce genetic variability.

• -Three types:– Stabilizing– Disruptive– Directional

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Selection• Stabilizing

selection eliminates those phenotypes most different from the norm, thus reducing the frequency of phenotypic extremes. (AA, aa)

• Directional selection eliminates one extreme and moves the population toward the other. (AA or aa)

• Disruptive selection eliminates average phenotypes and encourages the extremes. (Aa) This tends to result in distinct phenotypes in the same population.

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Hardy-Weinberg Equilibrium

• For all populations to maintain equilibrium (no changes in allele frequencies over many generations) all five conditions must be met.– large population (no genetic drift)– random mating – no mutations– no gene flow– no selection

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Hardy-Weinberg Equilibrium

• When one condition changes, the gene pool or allele frequency of the population will change.

• These changes result in different genotypes and phenotypes (increased variation) in the population.

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Hardy-Weinberg Equilibrium

• A population that is not in Hardy-Weinberg equilibrium will undergo natural selection because of genetic variation.

• Natural selection will ultimately favor the most fit individual(s) in the population.

• This will result in changes in a population over time- EVOLUTION OCCURS!

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Hardy-Weinberg Equilibrium

• How would a mutation cause changes in allele frequency in a population?

• How would this allow evolution to occur?

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Hardy-Weinberg Equilibrium• How would

a small population affect allele frequencies over several generations?

• How would this allow evolution to occur?

Cheetah

Page 17: Hardy-Weinberg Equilibrium -And how it affects evolution.

Hardy-Weinberg Equilibrium

• How would gene flow affect allele frequencies in a population?

• How would this allow evolution to occur?

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Hardy-Weinberg Equilibrium

• How would natural selection change allele frequencies in a population?

• How does this allow evolution to occur?

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Hardy-Weinberg Equilibrium• How would

choosing a mate change allele frequencies in a population?

• How would this allow evolution to occur?

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Mechanisms for Change

• When populations are not in Hardy-Weinberg Equilibrium, evolution occurs.

• The conditions that upset Hardy-Weinberg equilibrium are known as the mechanisms of change.

• Cause changes in alleles in a population.

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Mechanisms of Evolution• Genetic Variation

• Descent and the genetic differences that are heritable and passed on to the next generation;

• Mutation, migration (gene flow), genetic drift, non-random mating, and natural selection as mechanisms for change;

• Result in changes over time- Evolution!