Employing the toolkit in space and time: switches

Readings: Chapter 5 from “Endless Forms Most Beautiful”

Informational Questions (bring your answers to these questions, as you will be responsible for answering one of them at the start of class):

1. What is the “dark matter” in the genome? What is its function?

2. What is a genetic switch and what is its function?

3. Using Figure 5.1, would there be a change in the expression of the gene if the heart switch were removed? Why?

4. How does the author distinguish switches from signature sequences? What makes one genetic switch different from another? Who binds the signature sequence and what does it do?

5. How do the experiments described in Figure 5.4 suggest how changes in form might evolve?

6. How do Hox genes act to control switches that give the repeated modules in animals different form/function?

7. How can switches lead to differences in form between individuals in a species?

8. Why would alterations in one of the switches that controls the expression of a toolkit gene alter one structure but not others in an organism?

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:

9. (Group 1) How do switches convert spatial information into different domains of gene expression? To

illustrate the idea use figure 5.2 and predict what would happen to gene X expression if repressor B was not

present in the embryo.

10. (Group 2) 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?

11. (Group 3) Which aspect of the genome/ (switches or toolkit genes) do you think contain the instructions for building animal form? Why?

12. (Group 4) Would distinct, but related species (example-humans and chimpanzees) more likely have different switches or different toolkit genes? Why?