Two parents who do not have sickle cell anemia have a child that has the disease. The parents are both:

Question

A.  homozygous for the sickle cell allele.
B.  heterozygous for the sickle cell allele.
C.  homozygous for the normal allele.
D.  epistatic for the sickle cell allele.
E.  pleiotropic for the sickle cell allele.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

  Gather Content
· What do you already know about sickle cell anemia? How does it relate to the question?

  Consider Possibilities
· What other information is related to the question? Which information is most useful?
   Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  heterozygous for the sickle cell allele.

Clarify Question
· What is the key concept addressed by the question?
        o The question stem is asking you to determine the genotype of parents when you know the parent’s and offspring’s phenotypes.
· What type of thinking is required?
        o This question is asking you to take the concept of allele dominance and use, or apply, it to identify genotypes of individuals.
· What key words does the question contain and what do they mean?
        o Sickle cell anemia, which refers to a hereditary disease affecting hemoglobin in humans.
        o Homozygous, which means that both alleles for a gene are the same.
        o Heterozygous, which means that the alleles for a gene are different.
        o Epistatic, which is the phenomenon in which an allele for one gene may have different effects, depending on alleles present at other genes.
        o Pleiotropic, which means alleles affect multiple aspects of a phenotype.

  Gather Content
· What do you already know about sickle cell anemia? How does it relate to the question?
        o The sickle cell allele is recessive to the normal allele. This means that only individuals that are homozygous recessive will express sickle cell anemia.

  Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o Epistasis is the phenomenon in which an allele for one gene may have different effects, depending on alleles present at other genes. In addition, pleiotropic alleles often affect multiple aspects of a phenotype. When would a gene be either epistatic or pleiotropic?
   Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Recall that Punnett squares may be a useful tool for determining the genotype of parents and offspring.  Perhaps the creation of Punnett squares will be a useful tool for determining the genotype of the parents based upon their phenotype.
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to determine the genotype of the parents.
        o Answering this question correctly depended on your ability to use Mendelian geneticsin a new situation.
        o If you got the right answer correct, great job! If you got an incorrect answer, where did the process break down? Did you remember how dominant and recessive alleles are expressed as phenotypes? Do you understand the difference between an organism’s genotype and an organism’s phenotype? Did you have trouble extending the application of Punnett squares to answer this question?