List five differences between early development in mammals as compared with other vertebrates. Be specific. (10 pts)Compaction of the embryo, Very slow cell divisions (12-24 hrs), Early MBT, Two organizing centers(node and AVE),

Rotational cleavage, very small size,, two distinct early tissue types: trophoblast and icm, internal development

3a. Describe the process of secondary neurulation, at the cellular/tissue level. (5 pts)b. Where does secondary neurulation occur? (2 pts) At the posterior of the embryo

c. What tissue is most directly required to induce secondary neurulation? (2 pts) notochord

4. In C. elegans, the identity of the cell that is the precursor of the germline is determined by the presence of P granules. The P granules are actively transported into only one cell during each cleavage division.a. What are the two general mechanisms that can be used to divide components of the cell during? (4 pts)actin-based microfilaments and tubulin-based microtubules move components around the cell

b. How would one test which of these two mechanisms is used for segregation of specific components? Be specific and be sure to describe the possible results and their interpretations. (6 pts)One can add a specific inhibitor to the developing embryo (colchicine or nocodazole to inhibit tubulin polymerization, or cytochalasin B to inhibit actin polymerization) and ask whether the P granules move to the posterior cell or not. If colchicine inhibits the movement, but cytochalasin B does not, then tubulin-based microtubules must be responsible for P granule movement. If the reverse occurs, then actin-based microfilaments are responsible.

c. Which mechanism is used for transport of the P granules? Actin-based microfilaments d. In development of an embryonic axis of Drosophila, segregation of cytoplasmic components is also important. Which axis is

determined in this way, what are the cytoplasmic components that are segregated, and where do they go? (6 pts)During A/P axis formation, Drosophila bicoid mRNA is transported to the anterior pole while nanos mRNA is transported to the posterior.e. Which mechanism is used for transport of the cytoplasmic determinants in the Drosophila egg? (2 pts)

tubulin-based microtubules

5a. What are the names of the classes of genes used to specify regional (segmental) identity in mouse and flies? (Give one name used to describe the fly genes and for mouse) : Homeotic selector genes in flies, Hox genes in mouseb. Describe three ways in which the genes that specify regional identity in these organisms are similar. (9 pts)

Similar in protein structure (all are homeobox transcription factors) Similar in distribution in the genome (found in clusters) Similar in distribution of expression within the organism (Most 3’ expressed most anteriorly to most 5’

expressed most posteriorly)7-. Name the four classes of genes that produce the segmentally reiterated pattern in the Drosophila embryo and indicate the order in which they are active. 1.Maternal genes 2.Gap genes 3.Pair-rule genes. 4.Segment polarity genes