sukhs
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24. The parents of a son with Duchenne muscular dystrophy
(DMD) are planning to have a second child by in
vitro fertilization. Several viable embryos from the procedure
are produced. The mother does not carry any of
the known mutations in the dystrophin gene, and DNA
testing on four of the best embryos is done using a
restriction fragment length polymorphism (RFLP) that
is informative in this family. On the basis of the results
shown below, what is the best conclusion about the
embryos?
(A) Embryos 2 and 4 will produce children with DMD
(B) Embryo 3 will produce a child with DMD
(C) Only Embryo 4 will produce a child with DMD
(D) Embryo 1 is a carrier of the DMD allele
(E) Three embryos will produce unaffected children
Attached Files:
question.bmp (1338 KB, 183 downloads)
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| babydoc4usmle
Forum Guru
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is it my eyes or those bars are actually different sizes? is that important?
anyways, it seems to me that it'a A
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| sukhs
Forum Senior
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Posts: 169
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hi babydoc...
good try but can u plz explain the answer ,how A???
the size if the lines does not matter,its jst my mistake..
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| babydoc4usmle
Forum Guru
Topics: 18
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well, i looked at the pattern of affected child and compared to the embrios
2 and 4 have same patterns with affected child
since you asked i feel it was wrong answer
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| sukhs
Forum Senior
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ok babydoc
good u tried
but yes
dats not the right answer
so now we have 4 choices to ans from?
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| babydoc4usmle
Forum Guru
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then my second choice is D
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| sukhs
Forum Senior
Topics: 13
Posts: 169
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hi babydoc
u r the only 1 hu tried
well,
here is the answer
i got it wrong too
24. The correct answer is E. Duchenne muscular dystrophy
(DMD) is an X-linked recessive disease typically affecting
males. Females who inherit the disease-producing
gene are usually unaffected carriers. In this family, the
mother is a carrier of the DMD gene. Comparing her
RFLP pattern to her affected son shows that the top (larger)
fragment in her pattern is a surrogate marker for the
DMD gene. The lower (smaller) fragment in her pattern
is a surrogate marker for her normal allele. (Note that in
the unaffected father, genetically unrelated to the mother,
the top fragment is a marker for his normal gene.) Three
embryos will produce phenotypically unaffected children:
Embryo 1 (a female homozygous for the normal allele),
Embryo 3 (a male), and Embryo 4 (a female carrier).
Only Embryo 2 will produce a male with DMD.
Embryo 4 will produce a carrier female who is not
affected (thus eliminating choices A and C).
Embryo 3 (choice B) will produce a normal male without
the DMD allele.
Embryo 1 (choice D) will be a female carrier of the DMD
allele. Embryo 1 is homozygous for the normal allele.
and i still cant quite get it though
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| babydoc4usmle
Forum Guru
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well i still don't understand, they said the mother is normal (genetically, not phenotipically)
anyways....it's too late for me
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| thornflier
Forum Newbie
Topics: 4
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didn't get it.... how could you guys know that 2 is male and 4 is female??
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| babydoc4usmle
Forum Guru
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this is another point i didn't understand
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| indidoc1
Forum Guru
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babydoc4usmle wrote:well i still don't understand, they said the mother is normal (genetically, not phenotipically) anyways....it's too late for me
Exactly my point
If the mum ws genetically normal, there should never have been any case of duchene's.
I guess there's something amiss.
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| indidoc1
Forum Guru
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i ll explain y in a while... 1st lemme put down my thoughts... or i ll forget them..
Embryo 1 is a girl
Embyo 3 is a boy
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"Whether you think you can or whether you think you can't, you're right!" ~ Henry Ford
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| indidoc1
Forum Guru
Topics: 50
Posts: 978
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further...
1=normal
3=normal
AAAARRRRRGGGHHH!!
This is driving me crazy.. n its pretty late at my end.. will try 2moro.
Basically, i hv managed to rule out choices B&D so far... rest later.
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| mytime
Kick my butt!
Topics: 39
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E.haven't looked at theattachment but it's e. coz it's an X linked disorder. Something to do with the barr chromosome i suppsose.
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| extrapyramidal
Forum Newbie
Topics: 4
Posts: 28
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thickness of the lines matter from what i remember from genetis (kap).can you repost the pic with the thickness almost the same as the qustion...please....
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| indidoc1
Forum Guru
Topics: 50
Posts: 978
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yup thickness does matter,
in fact, i think 4 is a bit thicker than 2 (meaning 2 X chromosomes with top bar frm both mom n dad ) ---- carrier female
n 2 is comparatively thinner.... if its 1 X n that too the top 1, is the diseased one frm mom n its a boy...
This is the only explanation i cn think of... n i hv busted my brains over this...
So..
1=female... normal
2=male...diseased
3=male...normal
4=female...carrier
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| indidoc1
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here's a figure to explain it a lil better .. sorry fr my crude drawing
Attached Files:
x.JPG (30 KB, 28 downloads)
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| indidoc1
Forum Guru
Topics: 50
Posts: 978
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At least tell me if i ws right or wrong in what i did..
No responses in 2 days
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"Whether you think you can or whether you think you can't, you're right!" ~ Henry Ford
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| babydoc4usmle
Forum Guru
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i am very confused about the whole thing, so i will not say if you are right or not, sorry.....
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| new_n_lost
Politically InCorrect
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Ok i guess we all r getting confused so the only person who without looking at the attachment came to the correct conclusion is Mytime. Can Mytime post the line of reasoning adopted while answering this question.
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| sukhs
Forum Senior
Topics: 13
Posts: 169
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hi guys
this question is one of the kaplans q bank assessment question....
i never it,it got me
and still now...
far from the understanding
actually thats the explainationkaplans have given...i posted this question here in order to seek some help in understanding but now i think as none of us is getting it,,,,,,the question might b wrong as in kaplans....
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