Gene Pools Hardy-Weinberg ... 15.3b Hardy Weinberg Equilibrium Hardy-Weinberg Equilibrium Section...

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Transcript of Gene Pools Hardy-Weinberg ... 15.3b Hardy Weinberg Equilibrium Hardy-Weinberg Equilibrium Section...

  • 15.3b Hardy Weinberg Equilibrium

    Hardy-Weinberg Equilibrium Section 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 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?

    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 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

    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!

    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.

    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 fur total # of foxes


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