1. Yourresearch group has been tasked to study the development of a newly identified sea creature. This creature was identified in a deep-sea exploratory mission and resembles the nematode C. elegans A. You observe the species under the microscope and notice that, upon fertilization, a cleavage furrow that extends through the entire egg forms and the embryo is split into two cells. A subsequent similar cleavage occurs in each cell resulting in a 4-cell, then 8-cell, then 16-cell embryo that is identical in size to the newly fertilized egg. What type of cleavage does this new species exhibit? B. You decide to perform some experiments and use a hollow glass needle to separate the 4-cell stage embryo into 4 cells. You observe the results and are astonished to find that 4 complete sea creatures are formed. What model of specification does this experiment support? Explain C. During your observations you notice that a yellow colored circular area repeatedly forms on the top-right of the embryos as they complete their blastula stage, right before gastrulation. The color disappears during gastrulation. You want to find out what happens to that area, what kinds of cells does it give rise to? Design and describe two experiments you can perform to answer this question 2. You are studying the role of your-favorite-gene, YFG, in mouse embryos. You have a variety of developmental genetics tools at your disposal. Use the information provided to answer the following questions A. Previous work has demonstrated that upstream of the YFG region, there are two enhancers One is a brain specific enhancer, the other one is a mammary gland specific enhancer. See image below. Describe two possible experiments that may have allowed previous researchers to obtain this information. (hint: Find it!) Brain specific enhancer Mammary gland specific enhancer YFG B. You wish to determine if expression of YFG is essential for proper brain development and for proper mammary gland development in mice. Your thesis advisor recommends using an existing mouse strain in which exons 1-3 of YFG are flanked by loxP sites, and upon Cre recombination, will be excised leading to no functional YFG protein being produced. You have searched the literature for existing Cre recombinase mouse strains to cross this “floxed” (flanked by loxP sites) line to (hint: Lose it!) loxP binding sites for Cre recombinase Brain specific enhancer Mammary gland specific enhancer YFG You have narrowed down your search to the following 3 lines. Describe at least one experiment you could conduct and what Cre line would you use and why? Expression of Cre recombinase in brain and mammary gland primarily, some expression in other tissues, including liver. WAP Cre recombinase Expression of Cre recombinase in mammary gland primarily, some minimal expression in other tissues, including salivary gland MMTV Cre recombinase Expression of Cre recombinase in brain, some minimal expression in other tissues, including adrenal cortex CALB2 Cre recombinase Take-Home Quiz #1 Dr. Visbal You want to find out what would happen if you mis-expressed YFG in a region where it is normally not expressed (liver). Describe how you could use the UAS-GAL4 system to accomplish this. You can design any possible mouse line that you wish (Hint: Move it!) 3.