15.3b Hardy Weinberg Equilibrium

Hardy-Weinberg EquilibriumSection 15.3b

H.G. Hardy

Wilhelm Weinberg

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)

total # of alleles in the gene pool

Gene Pool Practice15 peccaries in a population

BB or Bb = long bristlesbb = short bristles

If 6 alleles in the population are the b variety and 24 are of the B variety, what are the allele frequencies?

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

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

Genetic Equilibrium· allele frequencies remain constant· 5 conditions are required to maintain genetic equilibrium

1. very large populations2. no gene flow3. no mutations4. no sexual selection5. no natural selection

H-W Rules1. very LARGE population - genetic drift (random chance) has less effect on a large population2. 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 alleles4. 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

p + q = 1p2 + 2pq + q2 = 1

p = frequency of T (dominant allele)q = frequency of t (recessive allele)

p2 (p x p) = frequency of TT2pq (p x q) = frequency of Ttq2 (q x q) = frequency of tt

ALWAYS solve for "q" first!

H-W PracticeUse 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.

1. Find q2, the frequency of short fur (ff).

2. Find allele frequency of the recessive allele (f).

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.

Total # of foxes = __________

# of short furtotal # of foxes

q2

p + q = 1p2 + 2pq + q2 = 1

REMEMBERREMEMBER