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Kaplan Qbank Mutation Question

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SaintJude

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Hi,

So this question from the Kaplan Qbank is really confusing me. Could someone please help explain the solution? Thank you!

Passage paraphrase: Many different mutations in a gene can cause disease "A", and while half of the patients inherit the condition from an affected parent, half of the patients have a new mutation with no family history...

Question:
How would a spontaneous mutation yield disease in a patient?

A. A mutation in disease "A" during mitosis in a patient
B. A mutation in disease "A" during meiosis in a patient
C. A mutation in disease "A" during mitosis in the patient's parent
D. A mutation in disease "A" during meiosis in the patient's parent.

Solution is....



D. Why isn't it A?
 

chiddler

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It's not A because a single cell having disease A does not mean that the entire person has disease A.

For example, if one of your cells RIGHT NOW develop cancer, chances are your body will kill it off. For you to obtain inherited cancer, your parents must have had a mutation error in producing gametes. This is why D is the right answer: the parents must have had a mutation in meiosis.
 

Pisiform

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I don't know but A seems right. We are talking about a disease that can be the result from the parent (genetic) or by itself. Spontaneous mutation generally involves errors by the exonuclease in proof-reading during replication ,.... and if one cancer cell is produced ... it will divide uncontrollably ...
 

MedPR

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Seems like it could be A or D depending on what other information is provided. Are you sure there's nothing relevant in the passage?

Edit: Just based on how the question is phrased though, A seems like the better choice. A disease by spontaneous mutation in an existing patient would need to be mitosis. Spontaneous mutations can lead to diseases in offspring, but a spontaneous mutation in meiosis wouldn't lead to disease in your current patient.
 
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SaintJude

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I don't know but A seems right. We are talking about a disease that can be the result from the parent (genetic) or by itself. Spontaneous mutation generally involves errors by the exonuclease in proof-reading during replication ,.... and if one cancer cell is produced ... it will divide uncontrollably ...

I think the analogy to cancer may be misleading. The passage is specifically referring to an inherited disease--an autosomal dominant disease. What is a "spontaneous mutation" and why is often associated with a hereditary disease?
 

MedPR

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I think the analogy to cancer may be misleading. The passage is specifically referring to an inherited disease--an autosomal dominant disease. What is a "spontaneous mutation" and why is often associated with a hereditary disease?


All inherited diseases come from a problem in the parent. The answer then must be D. You can't inherit a disease from yourself, which would be the case with mitosis.
 
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chiddler

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I think the analogy to cancer may be misleading. The passage is specifically referring to an inherited disease--an autosomal dominant disease. What is a "spontaneous mutation" and why is often associated with a hereditary disease?

You can have inherited susceptibility to cancer.

If that doesn't make you happy replace cancer with any disease :p
 

Pisiform

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yepp A single, abnormal gene on one of the first 22 nonsex chromosomes from either parent can cause an autosomal disorder.
 

chiddler

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I don't know but A seems right. We are talking about a disease that can be the result from the parent (genetic) or by itself. Spontaneous mutation generally involves errors by the exonuclease in proof-reading during replication ,.... and if one cancer cell is produced ... it will divide uncontrollably ...

I don't think so. I mean suppose the single cancerous cell starves to death coincidentally or anything else that may occur disabling it.

Point is, a single diseased cell doesn't mean that the person has the disease. On the other hand, if it's inherited, that person is screwed.

Therefore, it is much less likely to be a somatic mutation. Mcat is generally "best answer" not "THE UNEQUIVOCAL UNARGUABLE PRESIDENT OF THE UNITED STATES ENDORSED ANSWER" xD
 

MedPR

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I don't think so. I mean suppose the single cancerous cell starves to death coincidentally or anything else that may occur disabling it.

Point is, a single diseased cell doesn't mean that the person has the disease. On the other hand, if it's inherited, that person is screwed.

Therefore, it is much less likely to be a somatic mutation. Mcat is generally "best answer" not "THE UNEQUIVOCAL UNARGUABLE PRESIDENT OF THE UNITED STATES ENDORSED ANSWER" xD

Well if the passage talks about an inherited autosomal disease, is there any other answer besides spontaneous mutation in meiosis of the parent?
 

MedPR

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While we're on this topic is it possible for spontenous mutation during meiosis to cause a disease in the individual (in addition to the offspring)?
 

chiddler

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While we're on this topic is it possible for spontenous mutation during meiosis to cause a disease in the individual (in addition to the offspring)?

No I don't think so because gametes are generally...expendable. Even with the most devastating mutations, gametes only function to transfer DNA to create a zygote with no direct effect on the host.
 

MedPR

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No I don't think so because gametes are generally...expendable. Even with the most devastating mutations, gametes only function to transfer DNA to create a zygote with no direct effect on the host.

Alright, that's what I figured. Thanks :)
 

SLC

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While we're on this topic is it possible for spontenous mutation during meiosis to cause a disease in the individual (in addition to the offspring)?

Nope, gametes are not technically self cells, they have 1/2 complement of self DNA, but play no role in forming tissues or organs. Their sole purpose is to be donated to the production of offspring, or to be degraded and the products recycled.
 

SLC

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Passage paraphrase: Many different mutations in a gene can cause disease "A", and while half of the patients inherit the condition from an affected parent, half of the patients have a new mutation with no family history...

Question:
How would a spontaneous mutation yield disease in a patient?

A. A mutation in disease "A" during mitosis in a patient
B. A mutation in disease "A" during meiosis in a patient
C. A mutation in disease "A" during mitosis in the patient's parent
D. A mutation in disease "A" during meiosis in the patient's parent.

Solution is....



D. Why isn't it A?

Can't be A because a mutation during mitosis would most likely either induce apoptosis of the cell, or be destroyed by the individual's immune system, or produce no noticeable effects at all. The exception being certain types of cancer, though this generally doesn't even occur during mitosis.

Can't be B because gametes (the product of meiosis) are not self cells (or cells at all for that matter), and are not integrated into self tissue.

Can't be C, do we need to explain this one?

Has to be D therefore because the result would be a sperm or egg potentially carrying a disease causing mutation to be expressed in the offspring produced.
 
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