sudipto1973
Forum Newbie
Topics: 4
Posts: 31
|
Q. An autosomal recessive condition occurs with a frequency of 1/625 among a particular Native Indian tribe. What is the approximate chance that the clinically normal sister of an affected person will have an affected child if she marries an unrelated man from the same tribe?
(a) 1/4
(B) 1/25
(C) 1/50
(D) 1/75
(E) 1/625
Please provide your answer with an explanation. It will be greatly appreciated
|
| almina
Forum Senior
Topics: 34
Posts: 99
|
answer - D - 1/75
Explanation:
sister has a brother which is recessive for disease - aa, meaning that his parents are both carriers(Aa). It means that the sister has 3 possibilities - either she is AA, Aa, Aa -- 2/3 probability of being a carrier. Sister's husband is phenotipically normal, so does't have a disease, but he has a chance to be carrier. His chance to be a carrier is 2/25(2pq). I f both parents of the child are carriers, he has 25% chance to have the disease - 1/4.
So: 2/3*1/4*2/25 = 1/75
Agree?
|
| sudipto1973
Forum Newbie
Topics: 4
Posts: 31
|
couldn't agree more. Thanks for the really good explanation.
|
| the_cyborg007
Forum Newbie
Topics: 1
Posts: 2
|
notations
probability of SHE to be carrier SC
probability of HE to be carrier HC
probability of HE to be very very seek HS
SC = 2/3 (like almina said)
HC = 2pq = 2*1/25*24/25 = 48/625
HS = 1/625 (from problem)
probability of the child to be seek
SC*HC*1/4 + SC*HS*2/4
=2/3*48/625*1/4 + 2/3*1/625*2/4
=24/(3*625) + 1/(3*625)
=25/(3*625)
=1/3*25
=1/75
I must be some kind of m.f. geneus!
|
|
| |
| | | | |
