Mechanisms of Evolution
Hardy-Weinberg Law
Hardy-Weinberg Law

The Hardy–Weinberg
principle

states that the genotype frequencies in a
population remain constant or are in
equilibrium from generation to
generation unless specific disturbing
influences are introduced.
Hardy-Weinberg Law

Hardy–Weinberg equilibrium is an
ideal state that provides a baseline
against which change can be
analyzed
Hardy-Weinberg Law


Genotype -This is the "internally
coded, inheritable information"
carried by all living organisms.
"blueprint" or set of instructions for
building and maintaining a living
creature.
Hardy-Weinberg Law

Population – all members of a
species living in one locale

The occurrence of evolution within a
population is established by
determining that the genetic makeup
of the population has changed.
Hardy-Weinberg Law
Most common conditions that cause a
change in gene pool frequencies





Mutation
Gene flow
Nonrandom mating
Size of population
Natural selection
Hardy-Weinberg Law

Mutations
Changes in the
way cells
function or
develop, caused
by an inherited
genetic defect or
environmental
exposure.
Hardy-Weinberg Law

Gene flow the natural transfer
of genes from one population
into the genetic makeup of
another population through
hybridization and interbreeding

migration or the dispersal
of seeds and pollen
Hardy-Weinberg Law

Non-random mating -Mating that has
not occurred due to chance, and
therefore has had human interference
Hardy-Weinberg Law
Population Size
 Population must of a sufficient
size so that the laws of
probability apply
Hardy-Weinberg Law

Natural selection – occurs when a
new variation arises that allows
certain members of a population to
capture more resources.
Hardy-Weinberg Law

Equation for calculating gene pool
frequencies
 p2
+ 2pq + q2 = 1
Hardy-Weinberg Law

p2 = frequency of AA



2pq = frequency of Aa



( homozygous dominant)
Two dominant alleles
(heterozygous)
Two different alleles one dominant, one recessive
q2 = frequency of aa

( homozygous recessive) two recessive alleles
Hardy-Weinberg Law

Remember:

Dominant phenotype characteristics are
displayed by both:

Homozygous dominant
( homozygous dominant)
Two dominant alleles
&
heterozygous genotypes
(heterozygous)
Two different alleles one
dominant, one recessive
Hardy-Weinberg Law
 Example: Determine the Population that is
heterozygous for white coat

*ALLELE FOR BLACK COAT IS RECESSIVE
Hardy-Weinberg Law

12 white

4 black
1. CALCULATE q2
*Count the individuals that are
homozygous recessive
*calculate the percentage of
the total population they
represent. THIS IS q2
4 of the 16 cats show the
recessive phenotype which is
25% or 0.25
q2 =.25
Hardy-Weinberg Law

12 white

4 black
2. Find q
Take the square root of q2 to
obtain q, the frequency of the
recessive allele
q =.5
Hardy-Weinberg Law

12 white

4 black
3. Find p
The sum of the frequencies of
both alleles =100%
We know
q =.5
So if p+q=1
( a population in genetic equilibrium)
Then p = .5
Hardy-Weinberg Law

12 white

4 black
4. Find 2pq
The frequency of the
heterozygotes is 2pq which is
the percent of the population
that is heterozygous for white
coat:
2pq= 2(.5) (.5) = .50
50% is heterozygous for white
coat
Hardy-Weinberg Law


In class today/homework:
Finding a frequency of certain allele.

Specific allele/ total population of alleles
Hardy-Weinberg Law
 WHY is this important????????
 Based on these equations, we can determine
useful but difficult-to-measure facts about a
population.
http://www.mnn.com/earthmatters/animals/blogs/100years-later-the-passengerpigeon-still-hauntsus#ixzz3Bc4dEeCH
Hardy-Weinberg Law
 WHY
is this
important????????



Cancer
Autism
Downs syndrome