robin082006
Forum Hero
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5. Chromosome analysis is carried out on the polar bodies of a woman for screening prior to in vitro fertilization. Polar bodies removed from some oocytes contain two copies of chromosome 21 while others contain no copies of chromosome 21. The woman displays none of the characteristics of Down syndrome and so the nondisjunction that resulted in this condition must have occurred in which of the following cells?
A. Primary oocyte in her mother's germline
B. Secondary oocyte in her mother's germline germline
C. Blastomere in her mother's germline
D. Primary oocyte in her own germ line
E. Secondary oocyte in her own germline
F. Blastomere in her own germ line
Give your explanation please
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| spjokes
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D
Rule out A & B because NONDISJUNCTION is spontaneous and it has nothing to do with her mother.
The same reason holds good to exclude C & F as well
Coming to D & E, rule out E because secondary oogenesis hasn't occured (CLUE- PRIOR TO IVF)
so the answer is D.
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| nadiabarati
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F
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| spjokes
Forum Senior
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Could you please explain how we would get a blastomere prior to IVF?
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| nadiabarati
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upon ovulation secondary oocyte which is stopped in the metaphase of second devision of meiosis is released and upon fertilization this devision is completed and become oocyte. So we use secondary oocyte in IVF.
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| nadiabarati
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sorry I wanted type E
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| spjokes
Forum Senior
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Secondary Oocyte will form its polar body only after fertilization with the sperm. Now we know that fertilization hasnt occurred, so the polar body should have come from primary oocyte only which is the site for nondisjunction.
Please read the last three lines in the link below:
http://distance.stcc.edu/AandP/AP/AP2pages/reprod...
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| nadiabarati
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thanks a lot spjokes for the kind help. You are right. Answer is D
Unfortunately HY doesn't say about polar bodies!
secondary oocyte COMPLETE the second division from metaphasis or start it upon fertilization??
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| rman
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Wow, great question!
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| docarchana
Forum Guru
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yep great stuff.
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