Doubt - Qn on achondroplasia genetics

[voicesinmyhead]

---

Members don't see this ad.

qn id 701 in Uworld.

An achondroplasic man who doesnt know his family h/o comes with a normal wife and asks about the chance that the kid will be achondroplasic too?

Answer is 50 % (result of AD inheritance)

But achondroplasia is acquired by sporadic mutation in 85% cases, and only the rest is AD.

Wouldnt the better answer be that the child wont get the disease?

 

[tranquilo]

The father already has the mutation. No need to consider spontaneous ways of acquiring it. Just apply the mode of inheritance (AD): one from mom and one from dad!

 

[voicesinmyhead]

Yeah, i was just wondering why the question has his unknown family history mentioned then.
Spontaneous mutations are not inherited, right?

 

[Bancrofti]

Yeah, i was just wondering why the question has his unknown family history mentioned then.
Spontaneous mutations are not inherited, right?

Probably an example of where over-thinking it can get us in trouble. Even if his achondroplasia is of the sporadic type, it isn't a somatic acquired mutation... He can still pass it on to his kids. So there is always a 50% chance of a child getting it.

 

[ulikedaggers]

qn id 701 in Uworld.

An achondroplasic man who doesnt know his family h/o comes with a normal wife and asks about the chance that the kid will be achondroplasic too?

Answer is 50 % (result of AD inheritance)

But achondroplasia is acquired by sporadic mutation in 85% cases, and only the rest is AD.

Wouldnt the better answer be that the child wont get the disease?

I think the key point here is that you assume normal patterns of inheritance unless otherwise specified.

 

[Flamen04]

The dude has the disease. He is a dwarf. All of his cells of his body have the mutation. The "sporadic mutation" bit mainly applies to mutation in the gametes of men of increasing paternal age.