ICQs19,20.ppt

How are these axons being guided? The Eph ligands must be attracting the nasal axons and repelling the temporal axons The nasal axons must be totally unresponsive to the Eph ligand The concentration of the ligand alone allows nasal and temporal axons to be targeted to different areas The concentrations of both ligand and receptor dictate where the axons are targeted A molecule that guides axon outgrowth can be inhibitory to one set of axons and excitatory to another because of Differences in numbers of receptors on the axons Differences in kinds of receptors on the axons Combinatorial control All of the above Class 19 ICQs 1. The initial positional information that ultimately helps to specify different segmental identities along the A-P axis of the Drosophila embryo is provided by: a. A gradient of one small-molecular weight morphogen across the entire A-P axis. b. Overlapping gradients of several diffusible transcription factors acting as morphogens. c. Signals between cells in the cellular blastoderm. 2. The gap genes, which specify broad regions of identity along the A-P axis between the two poles of the embryo are transcribed a. before cellularization of the blastoderm. b. after cellularization of the blastoderm. .5 pt .5 pt Class 20 ICQs 3. A human with Spondylocostal dysplasia probably: Doesn’t form any somites Forms the somites fine, they just don’t differentiate properly Forms somites, but they are highly disorganized Forms somites in the wrong temporal order Transplantation of presomitic region 4.. This transplantation experiment with pre-somitic axial mesoderm shows that regional identity of somitic tissues is established a. before somite formation b. after somite formation. c. during somite formation In a screen for Drosophila patterning mutants, you have found a mutant in which segments T2 and T3 appear to be fused together into a single larger segment, but other segments appear to be normal. The mutation causing this phenotype is likely to be in a(n): Egg polarity gene Gap gene Pair rule gene Segment polarity gene 1. The initial positional information that ultimately helps to specify different segmental identities along the A-P axis of the Drosophila embryo is provided by: a. A gradient of one small-molecular weight morphogen across the entire A-P axis. b. Overlapping gradients of several diffusible transcription factors acting as morphogens. c. Signals between cells in the cellular blastoderm. .5 pt Class 20 ICQs Why are only two segments affected? if mutation were in coding, all segments would be affected, so it must be in a regulatory region Transplantation of presomitic region (.5) This transplantation experiment with pre-somitic axial mesoderm shows that regional identity of somitic tissues is established a. before somite formation b. after somite formation. c. during somite formation The identity of segments is determined ______ segmentation in Drosophila, and ______segmentation in vertebrates before; after after; before before; before after,; after In Drosophila, segmentation happens ___________ and in vertebrates, segmentation happens ____________ a. From anterior to posterior, from anterior to posterior b. From posterior to anterior, from posterior to anterior c. All at once, all at once d. All at once, from anterior to posterior e. All at once, from posterior to anterior