Background information & discussion questions IMPORTANT: If you haven’t already done so, be sure to read the Introduction to Unit Discussions so you know how to participate effecti

Background information & discussion questions IMPORTANT: If you haven’t already done so, be sure to read the Introduction to Unit Discussions so you know how to participate effectively In class, you learned about several important examples of cellular induction. This is the process by which one population of cells sends signals to another population of cells to change their developmental fate. Examples we discussed included the dorsal lip of the blastopore in Xenopus, the development of the neural tube in chordates, and the differentiation of somites in vertebrates. In each case, the proper differentiation of cells and tissues depends on signals that come from neighboring cells and tissues. In this discussion, I will ask you to consider two
hypothetical experiments: Experiment 1 — dorsal lip transplantation You excise the dorsal lip from the gastrula of a newt (the donor), and add it to the opposite side of a very closely related newt gastrula (the host). The newts are so closely related that the signals from the dorsal lip (and the receptors) are nearly identical. Different newt species are used because it helps us distinguish donor cells from host cells. This experiment is shown below. NewtGastrula.jpgExperiment 2 — somite transplantation You take some of the medial portion of a somite that has just condensed and transplant it to the ventral portion of that somite. See the diagram below. Somite.jpg Questions What is the origin of chordamesoderm tissue and what is its role in a normal embryo? Note: this question is NOT asking about the function of a notochord. Given your answers to #1, what will happen to the bottom (purple) newt embryo in Experiment 1? Explain your answer briefly. What fate do you think the transplanted “yellow” somite cells will have in Experiment 2? Will they go on to become back muscles or bone? Explain your answer briefly. Completion Criteria: Answer each of the questions above based on what you’ve learned from your readings and the lectures. Reply to one of your classmates. In your reply, comment briefly on their reasoning and offer your opinion. If you’ve changed your mind about your own answers because of a classmate’s post, explain why. NOTE — you will not be able to see anyone else’s posts until you have posted your own answers.