In a large population of randomly reproducing rabbits, a recessive allele r comprises 80% of the alleles for a gene. What percentage of the rabbits would you expect to have the recessive phenotype?

Question

A.  4%
B.  32%
C.  64%
D.  80%
E.  100%

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 the Hardy-Weinberg principle? 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

C.  64%

Clarify Question
· What is the key concept addressed by the question?
        o This question is asking you to calculate various frequencies for a population in Hardy-Weinberg equilibrium. What are the formulas involved in calculating the frequencies for a population in Hardy-Weinberg equilibrium?
· What type of thinking is required?
        o This is an analyze question because you have to calculate various frequencies for a population in Hardy-Weinberg equilibrium.
· What key words does the question contain and what do they mean?
        o Dominant phenotype, which refers to the physical trait of a version of a gene inherited from a single parent.
        o Recessive allele, which refers to the physical trait of a version of a gene inherited from both parents.
        o Hardy-Weinberg equilibrium, which refers to populations whose genotype frequencies do not change from generation to generation.
        o Allele, which refers to a version of a gene.
        o Frequency, which refers to the number of times a particular event occurs in a sample.

  Gather Content
· What do you already know about the Hardy-Weinberg principle? How does it relate to the question?
        o To solve this problem you will need to apply the Hardy-Weinberg equations. Recall that there are two equations involved in the Hardy-Weinberg principle. One equation is p + q = 1; where p is the frequency of the dominant allele, q is the frequency of the recessive allele, and 1 is 100% of the alleles. The other equation is p2 + 2pq + q2 = 1; where p2 is the frequency of the homozygous dominant genotype, 2pq is the frequency of the heterozygous genotype, q2 is the frequency of the homozygous recessive genotype, and 1 is 100% of the individuals. How are these two equations related? How can we go from an allele frequency to a homozygous genotype frequency?
 
Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o The question provides you with the frequency of the recessive allele. If you know the frequency of the recessive allele, then how can you find the frequency of homozygous recessive genotype? What phenotype will be expressed by the homozygous recessive genotype?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o To answer this question you must determine how to calculate the homozygous recessive genotype frequency when you are given the frequency of the recessive allele. Keep in mind that you may have a dominant phenotype with either a homozygous dominant or heterozygous genotype. What genotype do you have if you express the recessive 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 frequency of the recessive phenotype.
        o Answering this question correctly depended not only on distinguishing between genotypic and phenotypic frequencies, but on your ability to break down, or analyze, phenotypic frequencies.
        o If you got the correct answer, excellent! If you got an incorrect answer, where did the process break down? Did you remember how to calculate the square root of a decimal? Do you understand that the recessive phenotype must have a homozygous recessive genotype? Therefore, the frequency of the recessive phenotype must equal the frequency of which genotype? Did you have trouble breaking down the Hardy-Weinberg equations to determine the correct answer?