humpf!!
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In the family represented by the pedigree, affected persons have a disease characterized by mitochondrially inherited late-onset optic atrophy. Assuming that the family and personal medical history of the partner is unremarkable, the risk for optic atrophy to develop in the male child of IV-9 is closest to:
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
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| mitty
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A it says mitochondrial inherited d/s.Affected fathers do not pass the d/s to their sons.
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| drsnq
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A..mitochonderial inheritence diseases male does not transfer this disease to their child because in sperm mitochondrial present in middle piece and only head penetrate to the ovem so only mothers mitochondrial further goes in the zygote..
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| robin082006
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A
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| drbin
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sorry i didnt get it. i thought it is E 100 % bs 3rd generation female is affected( with her partner devoid of disease) so the chances of her transmitting it to her male baby is 100 % right? pls correct me where I am wrong....
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| drbin
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I thought it is E 100%. Bs 3rd generation female is affected with her partner unaffected so the chances of her transmitting disease to her male baby ie 4th generation 9 is 100 % right? pls correct me if iam wrong...
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| rm
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E. because with mitochondrial inheritance, mother passes the trait to all her kids. so her boys will have the affected the x chromosome.
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| drbin
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pls explain the answer
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| robin082006
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A for sure
Mitochondrial inheritance occurs from disease mothers only. Children of diseasse Fathers do not develop disease.
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| drbin
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yea ofcourse but in 3rd generation 8 ie female is affected and definitely she will pass on her disease to 4th gen male child (iv-9) who is in Question, so his chances of affecting disease is 100%, is that correct?
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| elissa
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A 0% The question asks about the chance/risk of the OFFSPRING of a male (IV-9).
As it is a a problem due to inherited mitochondria, males CANNOT pass it on to their offspring.
Simplistically speaking, recall that in spem, the mitochondria are located where the energy is needed - in the "tail". The tail drops off at conception, so no male-donated mitochondria can enter the egg....cos they've already left.
The answer is actually in the question, like many other USMLE quests. Furthermore, in an exam situation, if you did not have a clue, you could have guessed A given the image provided.
drbin while the male child IV-9 has the mito from his mum, it would depend on the penetrance of the disease and also the proportion of mito affected when he was conceived....ie depends a bit on what happened at oocyte mitosis. ie it is unlikely that every single mitochondira will be affected
Hope that this is of some use.
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| vallia
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drbin, in the question they speak about chance of having disease of the child of IV-9 and not IV-9 himself.
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| drbin
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ok vallia then it is clear and the answer is obviously 0%. i was taking the question as the chance of having the disease in iv-9 himself. thanks everybody for correcting me.
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| elissa
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You're very welcome.......and I prefer the term "helping".
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| waqastariq
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just an information that I am surprized to know that nobody mentioned here..
its just that:
MOTHER's MITOCHONDRIAL GENES are the only ones that are transferred to its babies...so if mother has got some disease ....all of her offsprings will have the disease until and unless there occurs some mutation in its favour ....and thats very rare so it approaches 100%
the pedigree is evident of this fact....
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| waqastariq
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just another interesting fact...
that all the mitochondrial genes we got are supposed to be the same as EVE 
so we can trace back our ancestors using mitochondrial DNA ..... but still we use Y chromosome...
for tracking our ancestors.... thats called population genetics...
diseases on Y chromosomes will be only transferred from father to baby...and same is the case for mitochondrial DNA...
find out the reason for that :P
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| vallia
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what do you mean nobody mention it..it was said several times in this post
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| roume
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i agree to the mitochondrial genes traced to eve but considering the % of mutations that take place,i dont think the original set looked anything like the ones we have today..evident by the pedigree showing moms passing on the disease n sons of diseased dads being spared..proving the nondiseased status of their moms..lolz
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| Cedrick
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Thanks to all who have been there before me
just label it does not need NBME just a litle some some
as a title
Thank yeah Baby !
Choice A
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