Groupings
Species
 Orgs that may interbreed to
produce fertile offspring
Population
 Local group of
orgs of one
species
 Evolution = change in the
genetic makeup (allele
frequencies) of a population
Hardy-Weinberg Principle
Allele frequencies are constant
in a non-evolving population
Quantifying Evolution
Gene Pool

entire set of alleles present in the population
Evolution

change in frequency of alleles in the population
p = frequency of one allele (usu. dom.)
q = frequency of another allele (usu. Rec.)
p+q=1
Quantifying Evolution



p2 = frequency of homozygous dominants
q2 = frequency of homozygous recessives
2pq = frequency of heterozygotes
p+q = 1
2
p
+ 2pq +
2
q
=1
Hardy-Weinberg Probs
In
pea plants, the allele for normal height is dominant
over the allele for short height. In a pop of 1000, 490
are short. How many individuals would you expect to
be homozygous dominant? Heterozygous?
 q2
q
p
 p2
 2pq
=
=
=
=
=
.49
.7
.3
.09
.42
Hardy-Weinberg Probs
In
the US, 64% of people have free earlobes.
What is the frequency of the dominant allele?
 p2
 q2
q
p
+ 2pq
=
=
=
=
.64
.36
.6
.4
Hardy-Weinberg Conditions
Hypothetical conditions that
must exist in a population for
no
evolution
to
occur
(allele frequencies constant)
Population Characteristics
Hinder Evolution
Help Evolution
(Hardy-Weinberg Conditions)
(Natural Conditions)

POPULATION SIZE
Infinitely Large
 Small
 Genetic Drift
MATE SELECTION

Random Mating
 Natural
Selection
VARIATION OF ADAPTIVENESS
 Natural Selection
 Equal Survival
INTERACTION W/ OTHER POPS
 Gene Flow
 Isolation
DNA CHANGES
 Mutations
 No mutations
Genetic Drift
Random fluctuations in allele frequencies
Example:
2
red, 2 blue orgs seek shelter
 50% survive. All are red
 Blues eliminated by chance (17%)
4
red, 4 blue head for shelter
 50% survive. All are red
 Blues eliminated by chance (1.4%)
Genetic Drift

Bottleneck Effect
Founder Effect

Catastrophe cuts pop size



Decreased variety of traits
Altered allele frequencies
Genetic drift more likely

Small group emigrates
to new habitat
Gene Flow
Introduction
of new traits through immigration
May be beneficial or insignificant
New traits  altered trait frequencies

Practice
Within a population of butterflies, the color brown (B) is
dominant over the color white (b).
4% of all butterflies are white.
Calculate the following:
a) The percentage of butterflies in the population that are
heterozygous.
b) The frequency of homozygous dominant individuals.
More Practice
The allele for a hitchhiker's thumb is recessive
compared to straight thumbs.
In a population of 1000 individuals, 339 show
the dominant phenotype.
How many individuals would you expect for
each of the three possible genotypes for this
trait.