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Gene Pool
• The total collection of genes in a population at any given time.
• Consists of all the alleles in all of the individuals of the
population.
• Each allele has a frequency in the population, notated by a p
or a q
• p represents the frequency of the dominant allele.
• q represents the frequency of the recessive allele.
Gene Pool
Gene Pool
• 2 alleles for color
• p = dominant = black
allele
• q = recessive = white
allele
• Total alleles = 20
• p + q = 20
• p = 12
•q=8
Hardy-Weinberg Equilibrium
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Requirements:
Large population.
No gene flow (immigration or emigration).
No mutations.
Mating is completely random.
No natural selection.
The Hardy-Weinberg Equation
• Uses
• To calculate genotype and allele frequencies in a population.
• To determine if a population is in Hardy-Weinberg equilibrium.
• To estimate what % of a population is carrying the allele for a
recessively inherited disease.
The Hardy-Weinberg Equation
p2 + 2pq + q2 = 1 where…
p = frequency of the dominant allele
q = frequency of the recessive allele
p2 = frequency of the homozygous dominant genotype (AA)
2pq = frequency of the heterozygous genotype (Aa)
q2 = frequency of the homozygous recessive genotype (aa)
Example 1: As a class
• The incomplete dominant trait for flower color is controlled by
2 alleles:
• R = red
• r = white
• In a population of 500 flowers…
• 320 are red (RR), 160 are pink (Rr), and 20 are white (rr)
• Since each flower has two alleles for the trait, there are 1000
alleles in the population of flowers.
• Find p and q.
Example 2: Your Turn
• What are the allele and genotypic frequencies for a population
of 500 mice in which 245 are black (BB), 210 are brown (Bb),
and 45 are white (bb)?
Example 3: Slightly more
challenging
• What are the allele and genotypic frequencies for a population
of 1000 pea plants in which 750 have blue flowers (B) and 250
have white flowers (b)?
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f(bb) = 250/1000 = 0.25 = q2
f(b) = q2 = 0.25 = 0.5
Recall p + q = 1,  f(B) = 1 – q = 1 – 0.5 = 0.5
f(BB) = p2 = (0.5)2 = 0.25
f(Bb) = 2pq = 2(0.5)(0.5) = 0.5