Introduction to Genetic Analysis 587

Introduction to Genetic Analysis 587 - uniformly...

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Unformatted text preview: uniformly distributed throughout the oocyte and the syncitial embryo. However, translation of hb-m mRNA is blocked by a repressor proteinthe NOS protein product. This protein is encoded by the nanos (nos) gene. In the mother, nos mRNA is deposited at the pos- terior pole in the oocyte, through its association with the (plus) ends of microtubules (Figure 18-10c). At the time of its translation, NOS protein becomes dis- tributed by diffusion in a gradient opposite that of BCD. The NOS gradient has a high point at the poste- rior pole and drops down to background levels in the middle of the AP axis of the embryo (Figure 18-10d). NOS protein inhibits translation of hb-m mRNA, and the level of inhibition is proportional to the concentra- tion of NOS protein, producing the shallow gradient of HB-M protein from the anterior to the posterior of the embryo. How do the maternal bcd and nos mRNAs get teth- ered to opposite ends of the polarized microtubules of the oocyte and early embryo? The answer is that therethe oocyte and early embryo?...
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