nbme1 genetics - laura81

[ArchivalUser]

sorry I am not able to post the pedigree chart.hope you remember.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%

The chart shows 4 generations, first generation woman has disease, second gen 2 boys, 2 girls all 4 with disease. third generation..one girl has 1 boy and one girl , both sick.The fourth generation ..the girl has 2 girls and 1 boy(IV-9) , all 3 sick. and they are asking about the kid of the boy

[ArchivalUser]

E) i think this bc its a mitochondrail ds, and all the children of the affected mother are affected

[ArchivalUser]

a is the ans

[ArchivalUser]

AAAA (0%)

[ArchivalUser]

The answer should be AAA

[ArchivalUser]

can u please explain??

[ArchivalUser]

the disease is inherited via the mitochondria genetic information. If you remember embryology when the sperm and egg meet the head of the sperm which has no mitochondria fuses with the egg which has the maternal mitochondrial DNA. Therefore if the mother has the disease, since her mitochondtial DNA is always in the egg which gets fertilised she will passs the disease to all her children. However if a male has the disease he cannot pass it on because his mitochondria DNA does not accompany the genetic material in the nucleus of the sperm (the head). so mothers pass it on and fathers dont.
hope this helps

[ArchivalUser]

i agree its A..,but on the list of "right" answers for NBME form ,t sais its E..which doesnt make any sense...