Absence of bicoid mRNA from a Drosophila egg leads to the absence...

Question

Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene
a. normally leads to formation of head structures.
b. normally leads to formation of tail structures.
c. is transcribed in the early embryo.
d. is a protein present in all head structures.

Accepted Answer

Welcome back. Our next problem, says a female Drosophila has two mutant alleles of the bike Oid gene which acts as a Morfogen during Drosophila development and is essential for establishing the anterior end of the fly. Its larva will have and our choices include two tails and lack all anterior structures, normal head and tail. Two heads and lack all the posterior structures and none of the above. So there is a possibility there are no correct answers offered. So um we do want, when we look at this question it seems a little bit silly but in a test you're under pressure. We want to make sure we remember that the anterior end is the front or head end of the fly. That's what we're talking about. And as we recall from content videos the bike coi gene is distributed in an asymmetric fashion. It's concentrated the protein that comes from it is concentrated on one side of the embryo setting up this gradient and it kind of acts in two ways. Um it activates so turns up the translation of proteins involved in segmentation and in development of anterior structures. And then it also suppresses the translation of proteins involved in the development of posterior structures. So it kind of sets up to reverse gradients there to make sure that the embryo is developing with the head and the tail end and it is essential for the development of these anterior structures. So let's look at our choices to see what would happen to the offspring of a female with two mutant genes. So we look at choice a and it says they will have two tails and lack all anterior structures. Well indeed, we're missing this factor that's necessary develop those head structures so we will end up with an embryo with two tails and no head. So Choice A. Is the correct answer. Let's double check uh Choice. We know that choice D. Must be incorrect uh Since we do have at least one correct answer. So we can eliminate that choice. B. Says normal head and tail. Well that's not gonna happen. We're missing something that helps the head develop and finally Choice C. Two heads and like all the posterior structures. Well that is obviously the opposite of what's happening here. So we're going to eliminate that. So again, our correct answer is The offspring will have a two tails and lack all anterior structures. See you in the next video.

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