Salamanders normally go through a juvenile stage in which they have external gills. Most salamanders lose these gills when they develop into adults, but axolotl salamanders retain gills into adulthood by suppressing metamorphosis. This is an example of

Question

A.  gene duplication.
B.  co-opting a gene for a new function.
C.  homeosis.
D.  heterochrony.

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 heterochrony?
 
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

D.  heterochrony.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses heterochrony.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.
· What key words does the question contain and what do they mean?
        o Axolotl salamanders are an unusual species of salamander, known for their large, feathery external gills even in adults.
 
Gather Content
· What do you already know about heterochrony?
        o Heterochrony is a term for an evolutionary change that involved a change in the timing of development.
 
Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Are the axolotl’s gills an example of gene duplication? No, we have no reason to think that this feature involved gene duplication.
        o Are the axolotl’s gills an example of co-opting a gene for a new function? No, we do not know the genetic basis of this feature.
        o Are the axolotl’s gills an example of homeosis? No, because the anatomical feature did not change in location – it changed in timing.
 
Choose Answer · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Are the axolotl’s gills an example of heterochrony? Yes, because they changed in developmental timing.
 
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 concept is exemplified by salamanders that retain gills into adulthood.
        o The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that by keeping a juvenile feature, these salamanders are changing the timing of development, making it an example of heterchrony?