8. Examine the figures and statements below. Which one of the statements is corr

Question

8. Examine the figures and statements below. Which one of the statements is correct? a) caudal and hunchback mRNAs are evenly distributed in the b) Caudal and Hunchback proteins are evenly distributed in c) Bicoid protein promotes the transcription of the hunchback d) Bicoid protein represses the translation of the hunchback - bicoid oocyte, but bicoid and nanos mRNAs are located either anteriorly or posteriorly, respectively caudal the oocyte, but Bicoid and Nanos proteins are located either anteriorly or posteriorly, respectively gene in the anterior region of the embryo. mRNA in the anterior region of the embryo. Posterior Position in oocyte - Bicoid - Nanos Hunchback - Caudal Anterior Posterior Position in 2.5-hour embryo

Explanation / Answer

Ans 8: a.

To conclude on the answer we need only to consider the first 2 options since they are the ones that come the closest to concluding as per the graph and actual occurrence of events during and post-fertilization.

Caudal and hunchback mRNAs do not have any control on location and are thus evenly distributed in the entire region of the egg. The first graph clearly shows this. Option 1 first part is true.

Just after fertilization, there are gradients formed at the ends of the egg, in which nanos mRNA concentrates in the posterior end and bicoid mRNA concentrates in the anterior end. This is seen in the first graph. Option 1 second part is true.

Further on translation of the mRNAs into proteins the bicoid and nanos proteins build gradients in the anterior and posterior parts of the early embryo. This is seen in the second graph. Option 2 first part is proven false.

In the early embryo, bicoid protein blocks translation of the caudal mRNA and so as seen in the second graph we see less of caudal protein in the anterior part of the embryo. Second part of option 2 claims this but the first part of the option is wrong and so we cull this option.

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