Mutations in the DFNA20/26 locus, which codes for the actin gamma 1 protein, are associated with congenital deafness. An irate senator complains that government money is being wasted on studies of this mutant gene -- in yeast! "I am no biologist," says the senator, "but I am pretty sure yeast don't have ears." How do you respond?

Question

A.  "You are right, Senator -- yeast do not have ears. We should revoke the funding immediately."
B.  "We can learn valuable information about the structure of the mutant protein by expressing it in yeast. It is difficult to collect large amounts of actin from tiny hair cells, and unethical to collect it from human patients."
C.  "We can learn valuable information about the transcription of the mutant gene in yeast. It is much more difficult to study transcription in human cells."
D.  "We can learn valuable information about sound transmission through the mutant yeast. By placing a speaker against a yeast vial and recording sound from the other side, we can infer how the mutant actin affects sound waves."


Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

Gather Content
What do you already know about mutant genes? What other information is related to the question?

Choose Answer
Given what you now know, what information 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.  "We can learn valuable information about the structure of the mutant protein by expressing it in yeast. It is difficult to collect large amounts of actin from tiny hair cells, and unethical to collect it from human patients."

Clarify Question
What is the key concept addressed by the question?
        · Why study mutant actin in yeast?
What type of thinking is required?
            o This is an evaluate question because you have to weigh the logic and content of different responses to see which would be best to answer the senator.

Gather Content
What do you already know about mutant genes? What other information is related to the question?
        · You already know that mutations are changes in the sequence of DNA that encodes a protein. Sometimes a mutation causes a significant change in the structure of a protein, leaving it nonfunctional and potentially causing disease. We know that actin is an important component of the stereocilia of hair cells that are in the inner ear, which is why a mutation in actin gamma protein 1 is associated with congenital deafness. Because yeast and human are both eukaryotes and contain similar transcription and translation machinery, human genes can be added to yeast which will then result in the yeast translating the protein of interest. In addition, there is considerable homology between yeast and human genes. As yeast can be grown rapidly and inexpensively, this is a much easier means of collecting large enough amounts of the protein to study in the lab than in mammalian systems.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · The process of transcription is similar between yeast and human so it is not much more difficult to study transcription in human cells. The researcher is probably not interested in studying transcription per se anyway, but is interested in the function, or lack thereof, of the mutated protein. Studies sound transmission through the yeast does not make sense at all and has nothing to do with human deafness (as yeast do not have ears), but having yeast express the protein of interest is a good way to collect large amounts of the protein that would be very difficult to obtain from mammalian hair cells and unethical to obtain from human patients.

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 Answering this question correctly depended upon your ability to weigh or judge the validity of certain arguments for using yeast as a model organism for a human deafness gene. If you answered incorrectly, which answer did you choose? Did you think that it is more difficult to study transcription in human cells than yeast cells? Did you think that because the gene was involved with deafness that the answer had to be related to sound transmission?