A human autosomal recessive trait appears in 1 in 100 births. What percent of people are homozygous dominant for this trait?

Question

A.  0.01
B.  0.10
C.  0.18
D.  0.81
E.  0.90

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

D.  0.81

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 Autosomal, which refers to genes located on the non-sex chromosomes.
        o Frequency, which refers to the number of times a particular event occurs in a sample.
        o Heterozygote, which means the individual contains different alleles for the gene.
        o Carriers, which means the individual contains one deleterious allele and one normal allele for the gene.
        o Dominant allele, which refers to a version of a gene expressed as a phenotype even if the allele was inherited from a single parent.
        o Recessive allele, which refers to a version of a gene expressed as a phenotype only if the allele was inherited from both parents.
        o Hardy-Weinberg equilibrium, which refers to populations whose genotype frequencies do not change from generation to generation.
 
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 a homozygous genotype frequency to an allele frequency?
 
Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o The question provides you with two different numbers to calculate the frequency of an autosomal recessive trait. One of these numbers is the part of the population expressing the trait and the other number is total population. How can you calculate a frequency if you know the number expressing the trait of interest and the number for the whole population?
 
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 which genotype frequency you are given. 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?
        o How do you get from a value that is squared, like p2, to a value that is not squared but has the same variable, like p? What is the mathematical function involved in this process?
 
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 carriers, or heterozygous individuals.
        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?