Genetics question about flies

[omarski]

From Qvault:
Question: 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?

• The father of the fly is homozygous for the mutant gene.
• The mother of the fly is homozygous for the mutant gene.
• The fly is homozygous for the mutant gene.
• The mother and father are heterozygous for the mutant gene.
• The fly is heterozygous for the mutant gene.

Their answer: The bicoid gene in D. melanogaster is important because it is an example of a maternal effect inheritance gene. The expression of the bicoid phenotype is only dependent on the genotype of the mother. If a mother is homozygous for the mutant genotype than her offspring will lethally express the trait.

I'm confused why it's the second answer? If the mom was homozygous for the lethal mutant gene, wouldn't she be dead? I thought lethal genes means the child would have to have to be homozygous for the mutant for it to actually be lethal. That or a male, since the male only has one X.
I know I'm missing something though, help me out please.

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[recnepskraor]

If a particular gene is inherited by a maternal effect, the mother's genotype ONLY contributes to the genotype of her offspring; the offspring's genotypes are the mother's genotype. For an offspring to inherit the lethal expression of the bicoid phenotype, the mother's genotype must be homozygous dominant for the lethal phenotype as the gene is inherited through a maternal effect.

 

[pecansandies22]

The mother does not express that phenotype. Maternal effect inheritance is all based maternally aka the mother. The mother in this case is genotypically mutant (mm), however her mother was not genotypically mutant therefore able to pass on the genes which gave her a mutant homozygous genotype as mentioned before. This genotype expresses how the embryo develops. Just remember if you see maternal effects on the DAT the mother is passing on the phenotype it has nothing to do with the father.

 

[omarski]

The mother does not express that phenotype. Maternal effect inheritance is all based maternally aka the mother. The mother in this case is genotypically mutant (mm), however her mother was not genotypically mutant therefore able to pass on the genes which gave her a mutant homozygous genotype as mentioned before. This genotype expresses how the embryo develops. Just remember if you see maternal effects on the DAT the mother is passing on the phenotype it has nothing to do with the father.

So the mom is passing down a mutation that'll be lethal in terms of development and the baby fly wont make it out alive?
The mom acquired the mutation somewhere during her lifetime and now that she has the mutation, she'll pass it down to her baby and kill it?
Am I looking at this right?
Also, if she was heterozygous, does that mean that the offspring only have a 50% chance of getting it?
Thanks

 

[pecansandies22]

So the mom is passing down a mutation that'll be lethal in terms of development and the baby fly wont make it out alive?
The mom acquired the mutation somewhere during her lifetime and now that she has the mutation, she'll pass it down to her baby and kill it?
Am I looking at this right?
Also, if she was heterozygous, does that mean that the offspring only have a 50% chance of getting it?
Thanks

Close, the mother carrying a genotype that is homozygous mutant. when a mother has a mutant genotype the offspring receives "poor instructions" for development and will not develop into a living mature fly. The mother's genotype determines how the offspring will develop. If the mother was heterozygous all offspring will live without an increased chance death. This phenomenon can answer you question why the mother that has the mutant genotype did not die. She received one mutant from her mother and another mutant allele from her father causing her to be homozygous mutant genotype but while she was developing her mother had a heterozygous genotype which would not cause poor development within the offspring allowing her to live and pass on her mutant alleles as a lethal phenotype. Maternal effect is when phenotype of the offspring is determined by the mother. Hope this helps try not to think about basic genetics of mother and father

 

[omarski]

I appreciate the thorough reply. I think I get it now! I think looking up the initial term helped a lot as well, as I had never seen it prior to this question. Thanks a lot pecan and rec .