Download Population Genetics

Population Genetics
Hardy-Weinberg and More
Variation of Traits in a Population
• Bell Curve
– Extremes at each end
• Causes of Variation
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Environment and heredity
Mutation
Recombination
Random fusion of gametes
Allele frequencies and Gene Pool
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Total genetic information available in population
Allele frequency is determined by dividing number of
certain allele by total number of alleles.
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P+Q=1
– P = number of recessive/total number of alleles
– Q =number of dominant/total number of alleles
Predicting Phenotypes
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Phenotype frequency
• Equal to the number of individuals with particular
phenotype divided by the total number of individuals in
the population.
• Same principle as allele frequencies
• P2 + 2PQ + Q2 = 1
Hardy Weinberg Equilibrium
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Allele frequencies in a population remain the
same from generation to generation unless acted
on by outside influences.
Assumptions about an ideal “made up”
population that is not evolving
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No net mutations occur
Individuals neither enter nor leave the population.
The population is large
Individuals mate randomly.
Natural Selection does not occur.
What is Microevolution?
What is Microevolution?
• A change in the gene frequency of a
population
• Can be seen over short periods of time
– One generation to the next
– For example, the frequency of a gene for
pesticide resistance in a population of crop
pests increases
– There can be many reasons for microevolution
Disruption of Genetic Equilibrium
• Mutation
– Can produce totally new alleles for a trait
– Most are harmful but the beneficial ones are
important for evolution
• Migration
– Immigration: Movement of individuals into a
population
– Emigration: Movement of individuals out a
population
• This is gene flow, the process of genes moving from
one population to another
Disruption of Genetic Equilibrium
• Genetic Drift
– Allele frequencies change as a result of random
events or chance
– Small populations
• a) Founders effect
• b) Bottle neck
• Non-Random Mating
– Many species do not mate randomly
– Based on geographic proximity and similar physical
characteristic
Disruption of Genetic Equilibrium
Disruption of Genetic Equilibrium
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Natural Selection
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Stabilizing selection
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Directional selection
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Individuals with average form of trait have highest
fitness
Extreme forms have lower fitness
One extreme form has greater fitness then average
Disruptive Selection
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Either extreme have greater fitness
Disruption of Genetic Equilibrium
• Sexual Selection
– Colors
– Females choose males based on
certain traits
– Extreme traits give female
indication of quality of males
genes