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sukhs
Forum Senior  Topics: 18 Posts: 184 |
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, 203 downloads)
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babydoc4usmle
| Forum Guru  Topics: 18 Posts: 627
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 Topics: 18 Posts: 184
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 Posts: 627
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 Topics: 18 Posts: 184
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 Topics: 18 Posts: 627
then my second choice is D
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sukhs
| Forum Senior Topics: 18 Posts: 184
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 Topics: 18 Posts: 627
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: 9 Posts: 26
didn't get it.... how could you guys know that 2 is male and 4 is female??
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babydoc4usmle
| Forum Guru Topics: 18 Posts: 627
this is another point i didn't understand
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indidoc1
| IMG physician  Topics: 104 Posts: 2083
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
| IMG physician Topics: 104 Posts: 2083
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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indidoc1
| IMG physician Topics: 104 Posts: 2083
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
| Go Marching in! Topics: 40 Posts: 3161
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
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
| IMG physician Topics: 104 Posts: 2083
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
| IMG physician Topics: 104 Posts: 2083
here's a figure to explain it a lil better .. sorry fr my crude drawing Attached Files: x.JPG (30 KB, 38 downloads)
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indidoc1
| IMG physician Topics: 104 Posts: 2083
At least tell me if i ws right or wrong in what i did.. No responses in 2 days
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babydoc4usmle
| Forum Guru Topics: 18 Posts: 627
i am very confused about the whole thing, so i will not say if you are right or not, sorry.....
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NNL
| Awaitin The Unexpected  Topics: 779 Posts: 6613
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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