Download Population Genetics

Population Genetics Terminology
Population
Genetics
• Population Genetics = The study of all
the genetic traits in a population
Genetic Equilibrium
Genetic Drift
• Gene Pool = combined genetic makeup
of all the members of a population
Genetic Equilibrium
The Hardy-Weinberg Principle
• A constant state of allele frequency
• Population not evolving
• Allele frequencies remain stable
• This situation is also known as the:
States that
• Under certain conditions, allelic
frequencies remain constant from
generation to generation
• If any one condition is not met, genetic
equilibrium will be disrupted and the
population may evolve
HARDY-WEINBERG PRINCIPLE
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Conditions required to maintain
genetic equilibrium:
• No natural selection – all alleles must be
equally favorable
• Random mating
• No migration – no new alleles brought into
population
• No significant mutations – mutations would
introduce new alleles into population
NOTE: Evolution is a result of
disruption in genetic equilibrium
4 Ways to Disrupt
Genetic Equilibrium
• Mutation: introducing new alleles into a
population
• Natural Selection: acting on variations
– Directional selection
– Stabilizing selection
– Disruptive selection
• Genetic Drift
• Gene Flow
Genetic Drift
Example of Genetic Drift
• is an accidental change in gene frequency
• Sometimes, genetic equilibrium can be
• The Amish population originated from 30
upset by random events in the
environment (example: a fire)
• can greatly affect small populations that
originated from a small number of
ancestors, since the genes of the
ancestors represent a small fraction of the
gene pool of the entire species.
individuals, and has been isolated ever
since due to religious practices.
• One of these original settlers carried the
recessive allele for short arms and legs,
and extra fingers and toes
• Today, 1 in 14 Amish have this trait,
compared to 1 in 1000 in the rest of the
US
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Gene Flow
Review Questions
• The movement of individuals into or out of
1. List the conditions necessary for a
population to maintain genetic equilibrium.
a population changes the frequency of
alleles in that populations gene pool.
• When an individual leaves(emmigrates),
its genes are lost
• When an individual enters (immigrates),
their genes are added to the population
• Can greatly effect small populations, may
not have any effect on large populations.
2. Why would migration and mutation have
a greater effect on the gene frequencies
of a very small population than a large
one? Explain your reasoning.
Answers to Review Q’s
1. No natural selection, random mating, no
2.
migration, no significant mutations.
Rapid evolutionary change due to
migration and mutation is more likely to
occur in a small population because of
genetic drift and the limited number of
mates.
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