DAT Q-Vault Biology Test 6 Question 15

[Aromatic Amine]

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.

i chose the fly is homozygous for the mutant gene. my reasoning was that if the mother was homozygous for the mutant gene wouldn't she express the lethal gene and therefore not even be able to pass it on to the children (because she is dead)? i'm just a bit confused on this question.

but then again if the child was homozygous for the mutant gene was that passed on? i'm definitely overlooking some basic concept.

---

Members don't see this ad.

 

[hope_to_match]

Is it B?

 

[Aromatic Amine]

yeah sorry i forgot to say that the answer is B

 

[hope_to_match]

I don't know whether my explanation would be correct but that just was my reasoning : the mother has to be homozygous because one of the X will be inactivated and to reduce the chance of inactivating the X that has the gene we want both to carry it (i.e be homozygous) . Again- I am not sure whether my reasoning is correct so maybe anyone else can answer?

 

[Aromatic Amine]

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.

that's the answer from Q-Vault.

i don't understand how if the mother is homozygous for the lethal genotype how can she pass it onto her offspring. (it's a lethal phenotype so wouldn't she die from it?)

i've never heard of a question asking for a lethal genotype being passed on through maternal inheritance.

maybe i'm clutching at straws and just being an idiot

 

[hope_to_match]

Yeah I understand your reasoning and I am not sure how to go about answering that... Maybe someone else can shine some light on this question for us?

 

[getsome111]

if I remember correctly the bicoid gene is just a recessive trait that can be expressed in females, akin to a recessive disease allele, and I think that it just makes the females butt squished or something similar which results in a bunch of dead offspring because the eggs cannot develop properly because the mothers anatomy damages the eggs or something like this. I dont think it has anything to do with the actual genotypes of the progeny, hence the name maternal effect. The mother is the one effected, but the progeny suffer

 

[hope_to_match]

if I remember correctly the bicoid gene is just a recessive trait that can be expressed in females, akin to a recessive disease allele, and I think that it just makes the females butt squished or something similar which results in a bunch of dead offspring because the eggs cannot develop properly because the mothers anatomy damages the eggs or something like this. I dont think it has anything to do with the actual genotypes of the progeny, hence the name maternal effect. The mother is the one effected, but the progeny suffer

from what i learned in developmental bio is that the bicoid gene is responsible for determining the embryos body axis

 

[getsome111]

oh yeah, its been a long day, last day before my dat tomorrow. heres what I found on wikipedia

|The building-blocks of anterior-posterior axis patterning in Drosophila are laid out during egg formation (oogenesis), well before the egg is fertilized and deposited. The maternal effect genes are responsible for the polarity of the egg and of the embryo. The developing egg (oocyte) is polarized by differentially localized mRNA molecules.
The genes that code for these mRNAs, called maternal effect genes, encode for proteins that get translated upon fertilization to establish concentration gradients that span the egg. Bicoid and hunchback are the maternal effect genes that are most important for patterning of anterior parts (head and thorax) of the Drosophila embryo. Nanos and Caudal are maternal effect genes that are important in the formation of more posterior abdominal segments of the Drosophila embryo.[2][3]
In embryos from bicoid mutant mothers, the head and thoracic structures are converted to the abdomen making the embryo with posterior structures on both ends, a lethal phenotype.[2]



basically what I get from this is that, before the eggs are fertilized they contain only genes from the mother, those genes are the ones responsible for early development, sort of like how mitochondria are maternal in inheritance. and thus, if you've got the bad ones, youre toast. Which comes to the "apply your biology know how" question; if these genes are present and create machinery for the early zygote, how the hell does the gene get passed on anyways, well, I can only assume that (in a heterozygote female) the bicoid gene products must be transcribed from the a normal allele. and then those normal alleles lost as the egg sheds its extra dna, leaving only the mutant bicoid genes within the egg... I could be totally wrong and am totally beat, DAT tuesday wooo :/

 

[Aromatic Amine]

awesome. i guess it make sense now. i appreciate the effort that you guys put forth. thanks a lot!

 

[member012]

So I just took the datQvault Bio test with this question and I choose, "The mother and father are heterozygous for the mutant gene". My reasoning what that if the gene is lethal then the mother must not be homozygous. Well that logic would normally apply but not to a maternal effect inheritance gene. From what I have gleamed from some webpages, the maternal effect is essentially that early on in development an embryo is not producing its own mRNA, proteins, etc. It gets all that good stuff from mom. So if mom produces bad proteins associated with development, then the offspring will be mutated. Bicoid is the result of mama fly producing bad proteins that are lethal to her offspring, but not to her. So I guess she is sterile because her offspring do not develop properly. It requires mom to be homozygous because it is recessive and has nothing to do with the father or the offspring as it is referring to the proteins mom is producing and therefore her genotype.

Just a very tricky question that without taking a genetics class would be hard to get right. I think most people just saw that it was a "maternal" effect and picked the answer with "mother" in it. I doubt 57% of datQvault uses actually made it through all of that logic assuming my "logic" is correct.

Hope this helps.