The snakes include some rather short and some incredibly long species, with a variation from about 100 to over 300 vertebrae. What developmental mechanism is the best candidate for changing the number of vertebrae in evolution?

Question

A.  Changes in genes that lay down extracellular matrix in bone
B.  Changes in genes necessary for neural crest development
C.  Changes in genes that control mitosis
D.  Changes in the somitogenesis clock


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 the development of vertebrae? 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

D.  Changes in the somitogenesis clock

Clarify Question
What is the key concept addressed by the question?
     · This question is asking about the process of development that yields vertebrae.

What type of thinking is required?
     · Apply level:
       o You are being asked to take what you already know and use, or apply, it to the source of the diversity in the number of snake vertebrae.


Gather Content
What do you already know about the development of vertebrae? What other information is related to the question?
     · The notochord gives rise to the somites.
     · The vertebrae, in addition to other structures, are derived from the somites.


Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
     · The neural crest is unrelated to the development of the vertebrae.
     · Genes that control mitosis.
     · The extracellular matrix in bone is not a model for additional bone growth.
     · Since somites give rise to the vertebrae, a change in the somitogenesis clock, in other words the pace at which somites form, could change the number of vertebrae that form.


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?
     · Apply level:
       o Answering this question correctly depended on your ability to use the formation of vertebrae in a new situation. If you got an incorrect answer, did you remember that vertebrae are derived from somites, or that a variable number of somites would give rise to a variable number of vertebrae?