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Genetic Equilibrium
Chapter 16- Section 1
What is a population?
A group of individuals of the same species that
routinely interbreed
Population Genetics – the study of evolution from
a genetic point of view
Microevolution- the change in the collective
genetic material of a population
Biston betularia f. typica is the whitebodied form of the peppered moth
Biston betularia f. carbonaria is the blackbodied form of the peppered moth.
Variation of Traits within a
population
Within a population,
individuals will vary in
observable traits
Ex. Fish of a single
species in a pond will
vary in size
Few fish are very
short or very long
Causes of variation
Variations influenced by environmental factors
Ex. Amount or quality of food, sunlight, living space
Variations in genotype
1. Mutation – a random change in a gene
2. Recombination – reshuffling of genes in a
diploid
3. Random pairing of gametes – millions of
sperm are produced, 1 gets to fuse with egg
The Gene Pool
A population’s gene
pool is the total of
all genes in the
population at any
one time.
•
If all members of a
population are
homozygous for a
particular allele,
then the allele is
fixed in the gene
pool.
The Hardy-Weinberg
Theorem
Used to describe a non-evolving population.
Natural populations are NOT expected to
actually be in Hardy-Weinberg equilibrium
Deviation from Hardy-Weinberg equilibrium
results in evolution
Understanding a non-evolving population, helps
us to understand how evolution occurs
*Genotype frequencies in a population tend to
remain the same from generation to generation
unless acted on by an outside source
Conditions of the H-W
Theorem
1. Large population size
- small populations can have chance fluctuations in
allele frequencies (e.g., fire, storm).
2. No migration
- immigrants can change the frequency of an allele by
bringing in new alleles to a population.
3. No net mutations
- if alleles change from one to another, this will change
the frequency of those alleles
Conditions of the H-W
Theorem
3. Random mating
- if certain traits are more desirable, then
individuals with those traits will be selected and
this will not allow for random mixing of alleles.
4. No natural selection
- if some individuals survive and reproduce at a
higher rate than others, then their offspring will
carry those genes and the frequency will change
for the next generation.
•Hardy-Weinberg Equilibrium
The gene pool of a non-evolving population remains
constant over multiple generations; i.e., the allele
frequency does not change over generations of time.
•The Hardy-Weinberg Equation:
1.0 = p2 + 2pq + q2
where p2 = frequency of AA genotype; 2pq = frequency
of Aa plus aA genotype; q2 = frequency of aa genotype
Hardy-Weinberg Equilibrium
Population of cats
n=100
16 white and 84 black
bb = white
B_ = black
Can we figure out the Allele frequencies of individuals BB and Bb?