Evolution of animal form: changes in the toolkit

Readings: Chapter 6-7 from “Endless Forms Most Beautiful”

Informational Questions (bring your answers to these questions, as you will be responsible for answering one in class):

1. What is the Cambrian Explosion? Why is it called an Explosion?

2. What approach can be used to determine which genes and cells were present in ancient animals (called Urbilateria) that were present over 500 million years ago (prior to the Cambrian Explosion) despite a lack of fossils and their DNA?

3. What genes were in the ancestors of the animals seen in the Cambrian? What types of cells were present in these animals? Why do we think this?

4. How can Williston’s Law be explained by changes in the expression of the Hox tool kit genes?

5. What changes in the toolkit of development are thought to have led to the Cambrian Explosion?

6. How does duplication of structures/functional redundancy in form create opportunities for specialization? Give an example.

7. Why have snakes lost their forelimbs? What caused the changes you propose in your answer?

8. We currently do not know where the genetic changes occurred that led to the transition of vertebrate limbs into different types of wings. Where would you look in the genome to identify these changes?

Discussion Questions (we will consider these questions in class after talking about the Informational Question above) as a way to apply and explore the ideas presented in the reading:

1. (Group 1) How in studying the evolution of development is “the present the key to understanding the past”? Give examples.

2. (Group 2) How does the Hox gene Ubx function to make the forewings and hindwings different in flies, beetles, and butterflies?

3. (Group 3) Does the tool kit represent possibility or destiny?

4. (Group 4) What do you think would happen to the form of an embryo if (a) a signature sequence, (b) a switch, or (c) the protein coding sequence of a toolkit gene were deleted from the genome? Why?