namf
Forum Elite
Topics: 80
Posts: 312
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Hi!
Anyone able to tell me about RFLP--restriction fragment length polymorphism?
Here's the question from qbank that I'm having trouble getting:
Family with Down's kid. A cloned DNA fragment, when used as a probe reveals an RFLP near chromosome 21's centromere. 4 haplotypes exist: A, B, C, D. Dad has AC &, mom has BD genotypes. Affected kid has ABC. Where did nondisjnctn most likely occur?
a)Child in 1st mitotic div
b)Mother in 1st meiosis (meiosis I)
c)monther in 2nd ""
d)father in 1st """
e)father in 2nd ""
Can you teach this to me as to a highschooler? Thanks for the help!
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| Renegade
Forum Elite
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Posts: 171
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Hmm... So we have a kid with 3 21 chromossomes  . Obviously, unless one of them divided when no other was dividing, the extra chr must come from either mother or father. If all cells have 3 chromossomes, then we can rule out a) ( a)'s the least likely). Since kid has ABC, extra chromossome must be... father's 8-[ . Now, meiosis II is a mere mitosis of the «compromised» chromossomes (meaning it's already decided which homologue chromosome goes where), so if there was trouble here, the kid would have 2 chromossomes of the same kind (ABA or CBC) :idea: . So it must be meiosis I. I think I read somewhere that most problems happened during meiosis I, anyway.
Don't hesitate for a moment to correct this if you think it's wrong, tough. :-#
___________________
«The desire to take medicine is perhaps the greatest feature which distinguishes man from animals.» W. Osler
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| namf
Forum Elite
Topics: 80
Posts: 312
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Thanks Renegade
Your answer agrees with Qbank. I just continue to struggle with these genetics questions. Know any very simple and useful resources for practice?
Besides this board, which is excellent! :lol:
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| Malaysian
Forum Guru
Topics: 28
Posts: 778
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OK child is ABC...mom BD and Dad is AC.In down's syndrome there is trisomy and so the child will get to alleles from one parent and one allele from another parent.In this case AC has come from father while the B from mother.
Now in meiosis there are 2 stages.In meiosis 1 the cells become 23,2N from 46,2N.......while in Meiosis 2 from 23,2N to 23,1N
Therefore the problem should have taken place in Meiosis 1 as thats where a non-disjunction can lead to a trisomy(23,3N).If there is a non-disjunction in meiosis 2 it can only lead to a 23,2N which is not a trisomy.
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