The reduced-bony-armor allele of the Eda gene is present in only about 1% of marine populations, but is predominant in freshwater populations of stickleback fish. What can we conclude?

Question

_____    Bony armor increases fitness in the marine environment, but reduces fitness in the freshwater environment.
_____  Freshwater fish with more bony armor have higher fitness than freshwater fish with less armor.
_____  Bony armor is an environmentally-controlled trait, not a genetic trait.
_____  The allele arose after the divergence of freshwater sticklebacks.
_____  The freshwater environment caused a high rate of mutation in the DNA.

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 stickleback evolution?
 
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

__X__  Bony armor increases fitness in the marine environment, but reduces fitness in the freshwater environment.
_____  Freshwater fish with more bony armor have higher fitness than freshwater fish with less armor.
_____  Bony armor is an environmentally-controlled trait, not a genetic trait.
_____  The allele arose after the divergence of freshwater sticklebacks.
_____  The freshwater environment caused a high rate of mutation in the DNA.


Clarify Question
· What is the key concept addressed by the question?
        o This question addresses stickleback evolution.
· What type of thinking is required?
        o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
· What key words does the question contain and what do they mean?
        o Armor in stickleback fish refers to bony plates that protect the fish from predators.
        o The Eda (Ectodysplasin) gene is associated with reduced bony armor in freshwater sticklebacks.
 
Gather Content
· What do you already know about stickleback evolution?
        o The freshwater three-spine stickleback fish, originated after the last ice age from marine populations with bony plates that protect the fish from predators.
        o Freshwater populations, subject to less predation, have lost their bony armor.
        o The Ectodysplasin (Eda) gene is one of a few associated with reduced armor in freshwater sticklebacks.  
 
Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Can we conclude that freshwater fish with more bony armor have higher fitness than freshwater fish with less armor? No. The opposite would appear to be true, since the reduced-armor allele is at higher levels in freshwater populations.
        o Can we conclude that bony armor is an environmentally-controlled trait, not a genetic trait? No. Although the environment may influence the trait’s fitness, we are told that the Eda gene regulates it, therefore it is a genetic trait.
        o Can we conclude that the allele arose after the divergence of freshwater sticklebacks? No, it is present (albeit at low levels) in marine populations, so it isn’t brand new in the freshwater populations.
        o Can we conclude that the freshwater environment caused a high rate of mutation in the DNA? No, there is no evidence for that.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Can we conclude that bony armor increases fitness in the marine environment, but reduces fitness in the freshwater environment? Yes, this is the most parsimonious explanation. In the marine environment, higher predation may make the high-armor allele worth it despite the tradeoffs of slower growth. In freshwater environments, faster growth may be more important than protection.
 
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 we can conclude from the predominance of the low-body-armor allele in freshwater sticklebacks, but not in marine sticklebacks.
        o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that there was natural selection for the reduced-body-armor allele in freshwater populations?