Download Hardy-Weinberg updated 9

Describes how Mendelian inheritance
preserves genetic variation from one
generation to the next in populations
that are not evolving
 Population
whose allele and genotype
frequencies do not change
 Not
undergoing evolutionary change
 Provides
a mathematical model by which to
assess whether a population is in equilibrium
 Frequency



of alleles range from 0-1.
Dominant allele represented by p
Recessive allele represented by q
p + q must = 1
p
+ q = 1 can be expanded to describe the
relationships of allele frequencies to genotype
frequencies in a population

(p + q)2 = 12

p2 + 2pq + q2 = 1



p2 is homozygous dominant individuals in a population
2pq is heterozygous
q2 is homozygous recessive
Allele frequencies:
p
or q
 Only
begin with this
is you are given
allele %
 If
not, you must
calculate
Genotype frequencies:
 p2,
2pq, or q2
 You
will most likely
be given phenotype
frequencies


p2 + 2pq = dominant
phenotypes
q2 = recessive
phenotype/genotype
 Always
begin Hardy-Weinberg calculations by
determining the frequency of homozygous
recessive genotype
 Ex.
If 90/1000 individuals are homozygous
recessive, then q2 = 90/1000 = 0.09

if q2 = 0.09, then q = 0.3

If q = 0.3, then p = 1 – 0.3 = 0.7
 From
there, you can calculate the frequency of
homozygous dominant individuals

p2 = 0.7 x 0.7 = 0.49
 Then
you can calculate the frequency of
heterozygous individuals

2 pq = 2 x 0.7 x 0.3 = 0.42
 In
a given gene pool of wildflowers, 80% of the
alleles are red (R) and 20% are the alleles are
white (r).
 If
the population is in Hardy-Weinberg
equilibrium, what will be the genotype
frequencies for:



Homozygous dominant individuals
Heterozygous individuals
Homozygous recessive individuals
 One
out of every 10,000 babies in the US is
born with the metabolic disorder PKU,
caused by a recessive allele.
 Using
the H-W principle, what is the
frequency of carriers, heterozygous
individuals who do not have the disease, but
may pass it on to their offspring?
 Gives
us a basis of comparison over successive
generations
 If
allele or genotype frequencies deviate from
the values predicted by Hardy-Weinberg
principle, the population is evolving
 MICROEVOLUTION
 Random
 No
mating
net mutations
 Large
population size
 No
migration
 No
natural selection