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SQ4 - MCDB 112 W10 STUDY QUESTION SET#4(covers lecture...

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MCDB 112 W10 STUDY QUESTION SET #4 (covers lecture set #4) page 1 1. It is useful to figure out the “gene order” when you have encountered a suite of mutants, each defective in a different gene, that show the same phenotype (in this case, mislocalized P granules). You can hypothesize that they work in the same pathway. Assume that you have antibodies against each of the proteins (called MIV in this species) and can localize the proteins in wild type and mutant embryos. Based on the immunolocalization data below, place the MIV genes in an “order.” Embryo Localization of Genotype MIV-­૒1 MIV-­૒2 MIV-­૒3 Wild type miv-­૒1 -­૒/-­૒ miv-­૒2 -­૒/-­૒ miv-­૒3 -­૒/-­૒ UPSTREAM _______________-­૒-­૒>_______________-­૒-­૒> ________________-­૒-­૒> P granule localization Consider an embryo where both conditional and autonomous fate specification can occur, like in C. elegans . In this animal, you can generate mutants and analyze their phenotypes and you can also manipulate the blastomeres. As we discussed in lecture, the P lineage (germ line) is dictated autonomously by maternal determinants (“P granules”) that are asymmetrically distributed each cell division, explaining this early specification. Blastomere isolation experiments suggest that at the 2- and early 4-cell stage, however, only a few other cell fates have been specified. If either of the AB cells is cultured alone, they do not give rise to their normal fate mapped lineages and EMS gives rise only to MS, not to E lineages. It is possible to separate blastomeres at various times. When you do this, you get the following results: Time of separation % isolated EMS descendants (post 4 cell birth) exhibiting E fates 1 min 0 5 min 0.5 10 min 3 15 min 8 20 min 28 30 min 47 2. What is a reasonable (simple) explanation for these results?
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MCDB 112 W10 STUDY QUESTION SET #4 (covers lecture set #4) page 2 3. You set up the experiment diagrammed here. Based on your results, you conclude that at the 4-cell stage, the EMS cell requires a signal from its neighbor, the P2 blastomere, in order to give rise to both E and MS lineages. What (general) results must have you obtained when you set up the experiments (B and C), shown to the right, in order to make this conclusion? 4. How could you determine if the signal sent by P2 was membrane bound or soluble, without actually identifying (cloning, purifying) the signal? 5. Now you focus on 2 other cells, called VUa and VUp. Fate mapping and lineage analysis shows that one VU cell typically gives rise to primary vulva and the other to hypodermis, but if their positions are switched in very early development (as soon as they are born), there is no effect on the embryo (that is, they are initially equivalent in terms of their fate potential). The fates of the VU cells are determined via a conditional mechanism.
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