You dissect the brain of a mutant mouse and find that parts of the "white matter" look gray. What is a likely cause?

Question

A.  defects in myelination
B.  peripheral nerve damage
C.  oversized dendrites
D.  excess myelination
E.  excess neuronal proliferation

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain?

Gather Content/Choose Answer
· What do you already know about white matter? How does it relate to the question?

Consider Alternatives
· What other information is related to the question?

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

A.  defects in myelination

Clarify Question
· What is the key concept addressed by the question?
        o The question is asking about what structure makes “white matter” white in color and what would happen if this structure was disrupted due to mutation?
· What type of thinking is required?
        o This question is asking you to apply what you know about white matter to solve what mutation the mouse has.
· What key words does the question contain?
        o White matter, gray, mutant.

Gather Content/Choose Answer
· What do you already know about white matter? How does it relate to the question?
        o To solve this problem, you’ll need to apply your knowledge of the differences between white matter and gray matter. Recall that myelinated axons form white matter while unmyelinated dendrites and cell bodies form gray matter. Thus, the answer likely related to myelination.

Consider Alternatives
· What other information is related to the question?
        o Although not directly discussed in this chapter, in earlier chapters the concept of mutation was introduced. Remember that a mutation is the change of a gene, often resulting in the change of the structure of a protein. Structural changes in proteins often lead to the protein becoming non-functional. As myelination produces a white color, loss of this color (to gray) is likely due to the loss of a protein involved in myelination.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o At this point, you should have everything you need to know to answer the question. Since white matter has myelinated axons and gray matter has unmyelinated dendrites and cell bodies, you can deduct that the mutation that has caused the white matter to look gray has to do with myelination (answers A and D). If myelinated axons appear white, then excess myelination would make the brain appear white, but a defect in myelination would make the brain appear gray. Therefore answer A must be 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?
        o If you figured out the correct answer, excellent! Remember, if you practice how to analyze and solve problems they will lead you to the correct answer more often than not. If you arrived at an incorrect answer, did you remember that white matter is found in parts of the brain where axons are myelinated? Did you remember that mutation is gene change that can lead to defects in proteins?
        o Was it clear to you that the type of thinking needed to answer this question is to apply your knowledge to a new concept (in this case applying knowledge of myelination to a new mouse mutation)? Consider where in the problem solving process your thinking went astray.