Need help on qvault bio question~

[vlaura0214]

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Bicoid is an example of a maternal effect inheritance gene in D. melanogaster. Which of the following situations is absolutely necessary for the lethal expression of the bicoid phenotype?

7%
A:
The father of the fly is homozygous for the mutant gene.


55%
B:
[Correct]
The mother of the fly is homozygous for the mutant gene.


23%
C:
[Yours]
The fly is homozygous for the mutant gene.


12%
D:
The mother and father are heterozygous for the mutant gene.


3%
E:
The fly is heterozygous for the mutant gene.


So the answer is B, but I am a little confused by this. I understand that the offspring would have to get the gene from the mother, but if the mother is homozygous for the lethal gene wouldn't that result in death for her? How would she be able to reproduce? Or am I just missing something?

Thank you!

 

[KentUT]

I'm not sure exactly how the biology works, but from my genetics course I remember that in maternal Effect inheritance the genotype of the progeny doesn't associate with the lethal phenotype. If the mother is m(mutant) and +(wild type) the offspring will be normal. Period.However if the MOTHER is m/m (homozygous for mutant), all the progeny will be effected (the fathers genotype doesn't matter). I think it has something to do with the mother passing on mutant mRNA and proteins. The take home message though is, if mom isn't homozygous for the mutant, the progeny will be fine (even if he/she is m/m (which is why yours was wrong). But if the mom is m/m, then all the progeny are effected! Check out wikipedia.

Hope that helped

 

[KentUT]

Oh sorry, I didn't really answer your exact questions. I'll take a shot, but I'm not 100% sure. The mother could be normal with a m/m genotype. Reiterating what I said above if the mothers mother is m/+ and father is m/+, one of the offspring in this case is m/m. But since the mothers mother is not m/m it is NOT LETHAL. Now that the mother in the question (daughter of m/+, m/+) is m/m (normal) she can live and reproduce. However, all of her offspring will be effected regardless of her mates genotype.That's my best shot, PM me if still confused.