The gene Brachyury promotes development of the notochord and the vertebrae in vertebrate animals. Among the rodents, most species have a long tail, but capybaras have a very short tail. What is the most likely difference you might expect to see for the Brachyury gene in capybaras compared to long-tailed rodents?

Question

A.  A smaller range of gene expression
B.  Deletion of the gene
C.  Higher levels of expression
D.  An expanded range of gene expression
E.  Mutation to resemble the ascidian gene

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 gene Brachyury?
 
Consider Possibilities · Consider the different answer options. Which can you rule out?
 
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.  A smaller range of gene expression

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses the gene Brachyury.
· What type of thinking is required?
        o This question is asking you to weigh and judge, or evaluate, evidence to choose the best of the possible answers.
· What key words does the question contain and what do they mean?
        o The notochord is a flexible rod that forms in the vertebrate embryo, and eventually becomes part of the vertebrae.
        o Capybaras are two species of very large rodents native to Central and South America.
 
Gather Content
· What do you already know about the gene Brachyury?
        o Brachyury is a gene that encodes a T-box transcription factor that controls the expression of other genes.
        o Although it is also found in invertebrates, Brachyury is most well-known for its roles in development of the notochord and vertebrae.
 
Consider Possibilities · Consider the different answer options. Which can you rule out?
        o Is it likely that Brachyury has higher levels of expression? No, that would act to promote vertebral development, not inhibit it.
        o Is it likely that Brachyury has an expanded range of gene expression? No, that would act to promote vertebral development, not inhibit it.
        o Is it likely that Brachyury has been mutated to resemble the ascidian gene? No, that doesn’t make sense.
        o Is it likely that Brachyury has been deleted? No, because capybaras still have to form an embryonic notochord and the spinal column.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Is it likely that Brachyury has a smaller range of gene expression in capybaras? Yes. Reduction of the Brachyury expression pattern is one possible change that may have led to the shortened tail.
 
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 what is the most likely change that may have occurred to the Brachyury gene in tailless capybaras?
        o The question required you to weigh and judge, or evaluate, evidence to choose the best of the possible answers.
        o Did you recognize that the most likely difference would be a reduction in the range of expression of Brachyury, because the length of the vertebral column (which normally extends into the tail) is reduced?