Download Hardy-Weinberg Equilibrium Gene Pools Gene Pool Practice Hardy

15.3b Hardy Weinberg Equilibrium
Hardy-Weinberg Equilibrium
Section 15.3b
Gene Pools
· combined genetic info of
all the members of a
population
· allele frequency - measure
of how common a certain
allele is in a population
aka relative frequency
# of times an allele(T) occurs in a gene pool
compared to other alleles (t)
# of specific allele (T or t)
H.G. Hardy
Wilhelm Weinberg
Gene Pool Practice
15 peccaries in a population
BB or Bb = long bristles
bb = short bristles
If 6 alleles in the population
are the b variety and 24 are
of the B variety, what are the
allele frequencies?
total # of alleles in the gene pool
Hardy-Weinberg Equilibrium
· allele frequencies in a population will remain
constant unless one or more factors (5) cause
those frequencies to change
· populations NOT in H-W equilibrium are evolving
· all Populations almost all of the time are evolving
exception - Horseshoe crab
B=
b=
*allele frequency equals the # of times an allele occurs in a
gene pool divided by the total # of allele in the gene pool
Genetic Equilibrium
· allele frequencies remain constant
· 5 conditions are required to maintain genetic
equilibrium
1. very large populations
2. no gene flow
3. no mutations
4. no sexual selection
5. no natural selection
H-W Rules
1. very LARGE population - genetic drift (random
chance) has less effect on a large population
2. NO gene flow - gene pool must be kept together
and separate from other populations
no emigration (out) or immigration (in)
3. NO mutations - mutations lead to new alleles
4. NO sexual selection - all members of a population
must have equal opportunity to produce offspring
NO sexual selection (females can't be picky)
5. NO natural selection - no phenotype can have a
selective advantage (normal distribution)
15.3b Hardy Weinberg Equilibrium
H-W Practice
Use the H-W equation to calculate predicted genotype frequencies
for this population.
In a population of foxes, 600 have long fur and
400 have short fur.
REMEMBER
REMEMBER
Total # of foxes = __________
1. Find q2, the frequency of short fur (ff).
p+q=1
p2 + 2pq + q2 = 1
p = frequency of T (dominant allele)
q = frequency of t (recessive allele)
p2 (p x p) = frequency of TT
2pq (p x q) = frequency of Tt
q2 (q x q) = frequency of tt
ALWAYS solve for "q" first!
p+q=1
p2 + 2pq + q2 = 1
# of short fur
total # of foxes
2. Find allele frequency of the recessive allele (f).
q2
3. Use the equations p + q = 1 to find p (F).
4. Calculate the predicted genotype frequencies from the
predicted allele frequencies.
p2 = _________ or _________% of foxes have FF genotype
2pq = __________ or _________% of foxes have Ff genotype
q2 = __________ or __________% of foxes have ff genotype
5. Double check your work by plugging values into the
second equation.