1. Manipulate: The Hardy-Weinberg equation is p 2 + 2pq + q 2 = 1, where p = probability of D,
q = probability of d, p2 = probability of DD, 2pq = probability of Dd, and q2 = probability of dd.
A. Look under Show Hardy
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1. Manipulate: The Hardy-Weinberg equation is p 2 + 2pq + q 2 = 1, where p = probability of D,
q = probability of d, p2 = probability of DD, 2pq = probability of Dd, and q2 = probability of dd.
A. Look under Show Hardy-Weinberg quantities. Notice there are two terms: Dd•Dd
and DD•dd. Rewrite each of these in terms of the variables p and q.
Dd•Dd: The genotype percentages change very little over time. This
indicates that a population with 36% DD, 48% Dd, and 16% dd is in
Hardy-Weinberg equilibrium.
DD•ddThe genotype percentages change very little over time. This
indicates that a population with 36% DD, 48% Dd, and 16% dd is in
Hardy-Weinberg equilibrium.
Because this ratio is usually close to 4 when a population is in Hardy-Weinberg
equilibrium, finding the ratio can be used as a quick test to see if a population is in
equilibrium or not. (Note: In most populations, the ratio will range from about 2 to 8.)
2. Experiment: With Dd set to 0%, the initial value of Dd•Dd / DD•dd is 0. Click Begin,
Breed, and Hatch. Record the percentage of DD, Dd, dd, and Dd•Dd / DD•dd for 5
generations in the table below.
Calculate: What is the mean value of Dd•Dd / DD•dd? The genotype percentages
change very little over time. This indicates that a population with 36%
DD, 48% Dd, and 16% dd is in Hardy-Weinberg equilibrium.
While the value of Dd•Dd / DD•dd may vary a bit, it will tend to stay fairly close to the
expected value of 4 as long as a population is in Hardy-Weinberg equilibrium. If the value of
Dd•Dd / DD•dd differs significantly from 4 (for example, below 2 or above 8), it is a sign that
the population is not in equilibrium and selection may be taking place.
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