The finding that homeotic genes are present in both mammals and insects indicates that these genes must

Question

A.  control the same traits.
B.  be on the same chromosomes.
C.  have arisen very early in the evolutionary history of animals.
D.  have developed independently and simultaneously.
E.  have been transmitted into mammals by an insect bite.

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 homeotic 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

C.  have arisen very early in the evolutionary history of animals.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses homeotic genes.
· 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 Homeotic genes are the Hox genes, a set of highly conserved developmental regulatory genes found in all animals.
 
Gather Content
· What do you already know about homeotic genes?
        o The homeotic genes are a set of related genes with several unusual features.
        o Similar genes are found in all animals, including invertebrates like flies and vertebrates like mice and humans.
        o They are clustered in the genome, and the order of genes in the cluster is the same as the order of gene expression along the anterior posterior axis.
        o They are master regulatory genes. When their expression changes due to a mutation, a completely different body part can grow in the wrong place.

  Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Since homeotic genes are in both flies and mice, does that mean they control the same traits? No. For instance, Antennapedia controls wing development in flies, but the related gene does not grow wings in mice.
        o Since homeotic genes are in both flies and mice, does that mean they are on the same chromosomes? No, they can be on different chromosomes in different species. In fact, mice have four copies of the whole Hox complex.
        o Since homeotic genes are in both flies and mice, does that mean they developed independently and simultaneously? No, that is not a likely explanation.
        o Since homeotic genes are in both flies and mice, does that mean they were transmitted into mammals by an insect bite? No, that is not likely. Insect bites do not transmit DNA.
  Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Since homeotic genes are in both flies and mice, does that mean the Hox complex arose very early in the evolutionary history of animals? Yes! The Hox genes arose in a common ancestor of vertebrates and invertebrates.

  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 it means that insects and mammals share similar homeotic genes.
        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 both insects and mammals inherited their homeotic genes from an ancient common ancestor?