pedigree question

[akimhaneul]

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Why can't cystric fibrosis in this question be X linked recessive? Only males are affected and it skips generations.

The answer is D.

Thanks!

 

[theonlytycrane]

I'm actually confused by node (e). Does that guy adopt some kids or something?

 

[akimhaneul]

I'm actually confused by node (e). Does that guy adopt some kids or something?

I'm confused by node (g) too. why does it look like that? what does that mean?

 

[wizzed101]

Probably because the spouses are not considered and assumed to be non-carriers.
To your original question, it can't be x-linked recessive because otherwise, e would've been affected.

Those "rules" you learned are not rules but heuristics. They are some of those one weird tricks to make you pick the wrong answers 😉

 

[akimhaneul]

Probably because the spouses are not considered and assumed to be non-carriers.
To your original question, it can't be x-linked recessive because otherwise, e would've been affected.

Those "rules" you learned are not rules but heuristics. They are some of those one weird tricks to make you pick the wrong answers 😉

Why specifically e? Why not h?


Also is node g supposed to be just direct children?


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[wizzed101]

The pedigree branch starting from h does not contain any affected individual so you cannot say anything about h. However, e is definitely a carrier.

 

[akimhaneul]

The pedigree branch starting from h does not contain any affected individual so you cannot say anything about h. However, e is definitely a carrier.

If the disease was x linked recessive and if h had the disease, wouldn't the pedigree still make sense since the father can't make his daughters have disease by marrying a completely normal wife?

Just trying to make sure I got this haha

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[wizzed101]

It doesn't matter if h is the carrier or not, you cannot confirm or deny that possibility based on what is given.

Like I said, it's impossible to be x-linked because

Spoiler

the branch starting from e has an affected individual, plus the disease is clearly recessive, plus it is assumed that the spouse of e is not a carrier (hence not mentioned), one diseased allele must have come from e. If the disease was x-linked, the male e would've been affected.

 

[akimhaneul]

To your original question, it can't be x-linked recessive because otherwise, e would've been affected.

Ok great thanks! and for this conclusion you made here, e would have been affected if the disease was x linked recessive because carrier mother has one recessive allele that would affect half of the sons?

 

[wizzed101]

Because e is male so he only has 1 x chromosome, and you know that he must has the diseased allele, from his pedigree branch, you know that he must be a carrier. If it were x-linked, he must be affected.

The 1/2 rule is not foolproof; it's just a way to quickly arrive at the most likely answer. You still have to ascertain it by further analysis.

For this question, x-linked seems like the most likely but you cannot rule out autosomal. Further analysis crosses out x-linked.

The trick to answer these kind of question is not asking yourself "why A" but "why NOT A."

 

[laczlacylaci]

Because e is male so he only has 1 x chromosome, and you know that he must has the diseased allele, from his pedigree branch, you know that he must be a carrier. If it were x-linked, he must be affected.

The 1/2 rule is not foolproof; it's just a way to quickly arrive at the most likely answer. You still have to ascertain it by further analysis.

For this question, x-linked seems like the most likely but you cannot rule out autosomal. Further analysis crosses out x-linked.

The trick to answer these kind of question is not asking yourself "why A" but "why NOT A."

Please correct if I'm incorrect.

We always assume that if the spouse is not present, they must be unaffected? (I got that from your previous post)
(Trying to prove X-linked wrong, I have in my head: e=XAY and the e-spouse=XAXA)?

With XAY×XAXA, q=XAXA, q-spouse=XAY, so r must be XAY(unaffected) which doesn't match, and that's why we prove A incorrect.

1) It seems we had to assume the spouses are unaffected, is that true for all questions?

2) what is up with the g node?

 

[wizzed101]

Well, I am not sure what's up with that particular pedigree tree. The spouses should always be present. If the disease is rare/deleterious, always assume a random spouse is not a carrier. Of course, there are exception: the wife/spouse is q is obviously a carrier.

1) For rare/deleterious disease, yes. Unless you are told otherwise, i.e founder effect. But they will always give you enough info to make a reasonable judgment.
2)Probably incest 😛 Idk maybe they want to indicate that the children are very young compared to their siblings.

 

[andelJ94]

Well, I am not sure what's up with that particular pedigree tree. The spouses should always be present. If the disease is rare/deleterious, always assume a random spouse is not a carrier. Of course, there are exception: the wife/spouse is q is obviously a carrier.

1) For rare/deleterious disease, yes. Unless you are told otherwise, i.e founder effect. But they will always give you enough info to make a reasonable judgment.
2)Probably incest 😛 Idk maybe they want to indicate that the children are very young compared to their siblings.

This pedigree looks off, with mistakes and/or serious omissions in it. Where did this thing come from? It does not seem at all like something the AAMC would give.