HARDY WEINBERG

1. The Evolution of Populations

2. Population Genetics
The study of how populations change
genetically over time

3. Studying the genetics of a population
provides a foundation for evolution
Microevolution - the change in the genetic
makeup of a population from generation to
generation
Grass growing in soil
full of heavy metals
(from a mine)
Same species of grass,
cannot grow on metal
rich soil

4. Populations
 Localized group of the
same species that can
interbreed and
produce fertile
offspring
Liger - the result
of a cross
between a male
lion and a female
tiger - ligers are
sterile

5. Gene pool
All the genes (all
alleles of those
genes) present in a
population at any
given time

6. Allele frequency
How often a particular
allele shows up in a
population is the allele
frequency
What is the allele
frequency for “B’ in this
population?
There are 7 “B” out of
14 total alleles, so 50%

7. p = “A” and q = “a”
The sum of p & q = 100% of the alleles
p q

8. The Hardy-Weinberg Theorem
If allele
frequencies stay
the same from
one generation to
the next, then no
evolution is
occurring.

9. Hardy Weinberg Equation
A = dominant allele a = recessive allele
p + q = 1
p = frequency of A allele
q = frequency of a allele
p2 + 2pq + q2 = 1
Where
p2 = frequency of AA genotype
2pq = frequency of Aa genotype
q2 = frequency of aa genotype

10. H-W equilibrium:
1. The population is very large
2. Mating is random
3. no mutations
4. no migration (gene flow)
5. no selection
If one of these conditions is broken, an evolutionary
force is acting to change allele frequencies, and
the population may not be in H-W equilibrium.

11. Recessive allele – q = ___
Dominant allele – p = ___
Recessive phenotype – q2 = ___
Homozygous dominant – p2 = ___
Heterozygous – 2pq = ____
p2 + 2pq + q2 = 1p + q = 1

12. Quick Check
 Using the Hardy Weinberg
equation:
 What symbol is used to
represent the dominant allele?
 What symbol is used to
represent the recessive allele?
p
q

13. Quick Check
 Using the Hardy Weinberg
equation:
 What does p2 represent in a
population?
 What does q2 represent?
 What does 2pq represent?
The proportion of
homozygous
dominant individuals
The proportion of
homozygous
recessive individuals
The proportion of
heterozygous
individuals

14. Practice Problem
 p + q = 1 where p = “A” and q = “a”
p2 + 2pq + q2 = 1 where p2 = AA, 2pq = Aa, q2 = aa
Directions: For each problem:
 first determine what value(s) you are given and fill
those in the table
 next fill in the rest of the values
 third determine what value(s) are asked for and put
that answer in the answer box.

15. Practice Problem
A group of 100 people has 22 that cannot
taste PTC paper. Tasting is dominant (TT
or Tt) and not tasting is recessive (t)
What percent of the alleles in the gene
pool are “T” and what percent are “t”?
p = ______
q = ______
p2 = ______
2pq = ______
q2 = ______

16. Practice Problem
A group of 100 pugs has 4 with a lethal
recessive disease (aa).
How many pugs are carriers for the
disease (Aa)? p = ______
q = ______
p2 = ______
2pq = ______
q2 = ______

17. More problems
1. A population of hamsters has a gene
consisting of 90% M alleles (black)
and 10% m alleles (gray). Mating is
random.
 Determine the proportion of offspring
that will be black and the proportion of
offspring that will be gray.

18. More problems
2.You are working with pea plants and you
found 36 plants out of 400 that were dwarf.
 Calculate the frequency of the tall gene
 Determine the number of heterozygous pea
plants

19. 3. In humans, the ability to taste PTC is
inherited as a simple dominant
characteristic. Suppose you found out that
360 out of 1000 college students could not
taste the chemical.
 What is the frequency of the gene for
tasting PTC?
 Determine the number of heterozygous
students in this population.

20. 4. A type of deformity appears in 4% of a
large herd of cattle. Assume the
deformity was caused by a recessive
gene.
 Calculate the percentage of the herd
that are carriers of the gene.
 Determine the frequency of the
dominant gene in this case.

21. 5.Albinism is recessive to normal
pigmentation in humans. The frequency
of the albino allele was 10% in a
population.
 Determine the proportion of people you
would expect to be albino.

22. 6. It is known that 64% of a large population
exhibits the recessive phenotype of a
characteristic controlled by 2 alleles (one is
dominant over the other).
 Determine the following:
 The frequency of the recessive allele
 The percentage that are heterozygous for this trait
 The percentage that exhibit the dominant trait
 The percentage that are homozygous for the
dominant trait
 The percentage that have one or more recessive
alleles

23. 7. Assume you placed 50 pure bred black
guinea pigs (dominant) with 50 albino guinea
pigs (recessive) and allowed the population to
attain genetic equilibrium (over several
generations).
 Frequency of dominant allele – 50%
 Frequency of recessive allele – 50%
 Determine the proportion of the population
that becomes white.

24. Extra Credit Option
 Choose a simple
dominant/recessive trait
in humans:
 Tongue rolling
 Free vs attached
earlobes
 Widow’s peak
 Survey at least 50
people
 Determine p, q, p2, 2pq,
and q2 for your
population
Name Dominant
phenotype
Recessive
phenotype