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Genetic Equilibrium
Objectives
Identify the causes of genotypic variation
in a population
Explain Hardy-Weinberg genetic
equilibrium and what it is used for
Variation of Traits in a
Population
Population genetics is the study of
evolution from a genetic point of view
A population is a group of individuals of the
same species that can interbreed
Evolution is a gradual change in the
genetic material of a population
A population is the smallest unit in which
evolution occurs
Within a population, individuals may vary in
observable traits (phenotypes)
Variation of Traits in a
Population
Biologists use graphs to study the frequency
of traits
Graphs usually resemble a bell curve
Individuals at the ends of the bell curve exhibit
extreme variations of the trait
Individuals in the bell curve exhibit the typical
variations of the trait
Variation of Traits in a
Population
Causes of Variation of Traits
Some variations are influenced by
environmental factors, such as the availability
of food
Variation is often influenced by heredity
Usually both factors play a role
Causes of Variation of Traits
3 main causes of genetic variation
Mutation: results from flawed copies of
original genes
Recombination: reassociation of genes of a
diploid individual
• Caused by crossing over between genes of
homologous chromosomes
Random fusion of gametes: which sperm out
of hundreds of millions will fertilize the egg?
Allele Frequencies and the
Gene Pool
Genetic variation in a population is
studied by looking at the gene pool
Gene pool – all the genes for all of the traits
in a population
Allele frequency is the number of times,
or percentage, an allele occurs in a
population
Determined by dividing the number of a
certain allele (A) by the total number of
alleles of all types in the population (A & a)
Allele Frequencies and the
Gene Pool
Phenotype frequency is the number of
times a specific phenotype occurs in a
population
Hardy-Weinberg Genetic
Equilibrium
States that allele frequencies in a
population tend to remain the same from
generation to generation
Allows scientists to consider what forces
disrupt genetic equilibrium by providing
a model of how genetic equilibrium is
maintained
Usually does not occur in real
populations
Hardy-Weinberg Genetic
Equilibrium
5 conditions required to maintain genetic
equilibrium:
No mutations occur
Individuals do not enter or leave the
population
Population is large
Individuals mate randomly
Selection does not occur
Notes Review
Identify the causes of genotypic variation
in a population
Mutations
Recombination
Random fusion of gametes
Notes Review
Explain Hardy-Weinberg genetic
equilibrium and what it is used for
Hardy-Weinberg states that allele
frequencies in a population tend to remain
the same from generation to generation
It allows scientists to consider what forces
disrupt genetic equilibrium by providing a
model of how genetic equilibrium is
maintained