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1.    Maternal Effect Genes encode proteins that specify the Anterior-Posterior axis in the

Drosophila syncytial embryo. The mRNAs for these genes are deposited in the egg during oogenesis.

Morphogen gradients of bicoid and nanos protein are formed in the embryo.


Picture of morphogen gradient.



Briefly describe:

a.    how the gradients form     2 points

b.    the role of bicoid and nanos proteins in specifying identity along the A-P axis   2 points


2.    bicoid and nanos mRNAs are localized in the embryo through an element in the 3'UTR (untranslated region) of their mRNA. The experiment below illustrates that nanos directs specification of posterior/tail identity in the embryo.

Using the knowledge that the 3' UTR of each mRNA is essential for proper localization, describe an experiment to demonstrate that nanos specifies posterior fates in the embryo.

a.    Explain how the experiment is designed. 4 points

b.    The results of this experiment are shown in the figure below. Explain how the results support the conclusion that nanos directs posterior cell fate. 2 points

           Maternal effect bicoid mutation disrupts anterior organizer and specification of anterior structures experiment. The picture cannot be pasted.     

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