What would you predict about the presence of Hox genes in the last common ancestor of vertebrates and invertebrates? (Select all that apply)

Question

_____  The genes contained homeoboxes.
_____  The genes specified anterior-posterior development.
_____  If mutated, there would be an extra pair of wings and legs growing from the head.
_____  The genes were in four clusters.
_____  The genes were in anterior-posterior order on the chromosome.
_____  The genes contained a MADS-box.
_____  That ancient ancestor was too primitive to have Hox genes.

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 Hox genes?

  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__  The genes contained homeoboxes.
__X__  The genes specified anterior-posterior development.
_____  If mutated, there would be an extra pair of wings and legs growing from the head.
_____  The genes were in four clusters.
__X__  The genes were in anterior-posterior order on the chromosome.
_____  The genes contained a MADS-box.
_____  That ancient ancestor was too primitive to have Hox genes.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses Hox genes.
· 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 Hox genes are the homeotic genes, found in all animals, that specify anterior-posterior development.
        o The last common ancestor of invertebrates and vertebrates is the organism that existed  ~500 million years ago, before the lineages split. It was a worm-like marine creature.

  Gather Content
· What do you already know about Hox genes?
        o Hox genes are homeotic genes that specify anterior-posterior development.
        o The genes contain a homeobox, that encodes a DNA-binding homeodomain.
        o The genes are organized in clusters in the genome, in order according to their expression pattern from head to tail.
        o Mice have four copies of the cluster, but flies only have one.
        o Mutating Hox genes often results in phenotypes of body parts growing in the wrong place.

  Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Would the Hox genes of the last common ancestor have mutated to produce an extra pair of wings and legs growing from the head? No, because the last common ancestor didn’t have wings!
        o Would the Hox genes of the last common ancestor have been in four clusters? No, mice have four clusters but flies and many other animals do not.
        o Would the Hox genes of the last common ancestor have contained a MADS-box? No that is from a different set of genes, in plants.
        o Would the last common ancestor have been too primitive to have Hox genes? No. The Hox genes of other animals must have originated very early in animal evolution.

  Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Would the Hox genes of the last common ancestor have contained homeoboxes? Yes, because they do in flies, mice, and other animals.
        o Would the Hox genes of the last common ancestor have specified anterior-posterior development? Yes, because they do in flies, mice, and other animals.
        o Would the Hox genes of the last common ancestor have been in anterior-posterior order on the chromosome? Yes, because they are in flies, mice, and other animals.

  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 you can guess about the Hox genes in the common ancestor of flies and mice.
        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 you can assume the ancestor probably had all the features that are shared between flies and mice, but not the unique ones?