Download Population Genetics and Hardy Weinburg

Population Genetics and
Hardy Weinburg
Population Genetics
• Study of the allele frequencies in a given
population.
• Gene Pool – All the genes (alleles) in a
population
What alleles do you
see in this pig pop.?
Hardy Weinberg Equations
p+q=1
p = frequency of dominant allele
q = frequency of recessive allele
p2 + 2pq + q2 = 1
p2 = frequency or % homozygous dominant (AA)
2pq = frequency or % heterozygous (Aa)
q2 = frequency or % homozygous recessive (aa)
Let’s use Hardy’s rules to
calculate the frequencies of the
alleles and genotypes in a
population.
If a population has a recessive genotype
frequency of .36, what is the frequency
of the recessive allele?
1.
2.
What information did the question give you?
a. q2 = .36 (frequencies are usually written as decimals)
What information does the problem ask for?
a.
q
= .6
What if the problem ask for the dominant allele frequency?
P = 1-q = .4
What other information can be
determined?
• What is the frequency of the recessive
genotype?
• What is the frequency of the homozgyous
dominant genotype?
• What is the frequency of the heterozygous
genotype?
• Out of 100 individuals, how many will have
the dominant phenotype?
Now what? Why use Hardy
Weinberg equations?
• To be able to compare the initial allele
frequency with the final allele frequency.
Ex: The same population was analyzed 5
years later. 25% of the population
expressed the homozygous phenotype.
What is the frequency of the recessive and
dominant alleles now?
p and q are both .5
The population has changed….
Hardy-Weinberg Principle
• This principle will be maintained in nature only if all five
of the following conditions are met:
1. Very large population
2. Isolation from other populations
3. No net mutations
4. Random mating
5. No natural selection
If these conditions are met, the
population is at genetic equilibrium.
But…, populations are not isolated
from variation.
Frequencies can change depending
on the conditions that exist in the
environment.
If the frequencies in a population
change over time the population
has evolved.