Hardy-Weinberg and Genetic
Equilibrium
Page 400
A. Hardy-Weinberg Principle
• 1. States that allele
frequencies in a population
will remain constant unless
one or more factors cause
those frequencies to change.
A. Hardy-Weinberg Principle
• 2. When allele frequencies remain constant,
that is called genetic equilibrium (no
evolution).
B. Five Conditions
• 1. There must be random mating.
• 2. The population must be very large.
B. Five Conditions
• 3. There can be no movement in or out of a
population.
B. Five Conditions
• 4. No mutations.
• 5. No natural selection.
C. Solving Problems
• 1. Imagine a geneticist studies a trait with
alleles A and a.
C. Solving Problems
• 2. A is dominant and a is recessive. A survey
shows 4% of the population has aa and 96% of
the population has AA or Aa.
C. Solving Problems
• 3. The Hardy-Weinberg equation shows the
frequency of the dominant allele (A) as
“p” and frequency of the recessive allele (a) as
“q”. The sum must equal 100%.
–P+q=1
C. Solving Problems
• 4. Recall from punnett squares, crosses that
involve these alleles have 3 possible
genotypes: AA, Aa, aa
C. Solving Problems
• 5. Those genotypes are expressed by this
equation: p2 + 2pq + q2=1
– p2= frequency of AA homozygotes
– 2pq=frequency of Aa heterozygotes
– q2= frequency of aa homozygotes
– 1= sum of allfrequencies of all genotypes (100%)
D. Practice!!
• 1. In a given generation, we find that p=0.8
and q=0.2. How can you figure out the relative
frequencies of AA, Aa, and aa?
E. Conclusion
• 1. As long as the Hardy-Weinberg conditions
hold, neither the frequency of the genotypes
nor the frequency of the alleles (p and q) will
change from generation to generation.
Partner Problems!
• 1. In a given generation, we find that p=0.5
and q=0.5. How can you figure out the relative
frequencies of AA, Aa, and aa.
• 2. In a given generation, we find that p=0.1
and q=0.9. How can you figure out the relative
frequencies of AA, Aa, and aa
Challenge Problem
• 1. In a population of dragons, the allele for
blue scales is dominant over the allele for red
scales. After surveying one population, there
are 75% of dragons with blue scales and 25%
of dragons with red scales. What is the
frequency of the following genotypes:
– Homozygous Dominant
– Homozygous Recessive
– Heterozygous