determine the number of carriers for PKU in Corpus Christi later in the semester when they covered the Hardy-Weinberg Principle (also referred to as Hardy-Weinberg Equilibrium).

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCEPage 3“PKU Carriers” by David J. GriséQuestionsDefine symbols for the alleles at the gene locus for PAH and then answer the following questions:4. What are the genotypes of Jane’s parents?5. What are the genotypes of Jane’s brother and sister?6. What is Jane’s genotype?

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCEPage 4“PKU Carriers” by David J. GriséPart II –Hardy-Weinberg“Today we will start discussing the Hardy-Weinberg Principle or Equilibrium,” Dr Jones said toward the end of class. “The Hardy-Weinberg Principle or Equilibrium is often used as a basis of comparison. It is a null hypothesis. The allele and genotype frequencies in a population will not change over time if no evolutionary forces are acting on that population. I am out of time today; please work on the Hardy-Weinberg question set for Friday.”Jane and Amanda got together on Thursday night to discuss the questions due the next day. The first question was about the data needed to determine the number of carriers in the population. “Jane, what’s a carrier?” “My parents are carriers, Amanda. They don’t have PKU because they have a dominant allele that produces PAH, but carry the recessive allele that doesn’t make PAH.” “Hey, Jane, we know your parents are carriers. Can we count the number of carriers in the population and move on to the next question?” “What are you thinking, Amanda? For most people, you can’t know if they are a carrier or not.” “But, Jane, we do know if a person is a carrier or not. We know your parents are carriers. We can just count the number of carriers, and then divide by the number of people in the population to get the frequency of carriers and plug that number into the equation.” Questions1. Who is correct? Can Jane and Amanda directly count the numbers of carriers in a population? Why or why not?2. Can Jane and Amanda determine any of the allele and/or genotype frequencies in the population just by counting? If so, which one(s)?

NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCEPage 5“PKU Carriers” by David J. GriséPart III –CarriersAfter determining that Jane is correct and that they cannot directly count carriers in the population, Amanda opened her notes from biology lecture. Dr. Jones had told them that the Hardy-Weinberg Equation, the mathematical expression of the Hardy-Weinberg Principle, can be stated as:(p+q)2=1 or as (p2+ 2pq + q2)= 1“Jane, what the heck are p and q?” After consulting the text, Jane said, “I think I figured it out, p and q are allele frequencies. I think that in the case of complete dominance with two alleles, p represents the frequency of the dominant allele, and q represents the frequency of the recessive allele.”“Right, so with only two alleles, then p + q = 1. I still don’t understand how this is helpful because we can’t determine p