Hardy-Weinberg Equilibrium -And how it affects evolution.
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Transcript of Hardy-Weinberg Equilibrium -And how it affects evolution.
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.
Hardy-Weinberg Equilibrium
• Genetic equilibrium will not change over time-
• Frequencies in each successive generation will be the same as the original parent generation.
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
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.
Random Mating
• Individuals must randomly mate with other individuals within a population.
• Non-random mating will result in changes in allele frequency.
Non-Random Mating
• Types of non-random mating:– Assortative mating- choosing
mates with similar phenotypes
– Competition- some males compete for mates
Mutations
• Mutations- Spontaneous changes in an allele.
• Increase variation in a population when old alleles change into new alleles.
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.
Selection
• Natural selection tends to reduce genetic variability.
• -Three types:– Stabilizing– Disruptive– Directional
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.
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
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.
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!
Hardy-Weinberg Equilibrium
• How would a mutation cause changes in allele frequency in a population?
• How would this allow evolution to occur?
Hardy-Weinberg Equilibrium• How would
a small population affect allele frequencies over several generations?
• How would this allow evolution to occur?
Cheetah
Hardy-Weinberg Equilibrium
• How would gene flow affect allele frequencies in a population?
• How would this allow evolution to occur?
Hardy-Weinberg Equilibrium
• How would natural selection change allele frequencies in a population?
• How does this allow evolution to occur?
Hardy-Weinberg Equilibrium• How would
choosing a mate change allele frequencies in a population?
• How would this allow evolution to occur?
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.
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!