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
drk1980 Forum Guru
Topics: 147 Posts: 1,038
11/24/05 - 10:31 AM
#2
will try to attempt....
it cant be mother's germline.
so from her own germline it could be at the secondary oocyte stage when the polar body undergoes meiosis 2, and has a chance of non-disjunction.......not sure if those wud show up phenotypically!
so then, maybe non-disjunction at the blastomere stage otherwise called mitotic nondisjunction"(plz correct me) wud result in mosaicism, with some abnormal chromsomes ans some normal....and she cud escape being afflicted with the syndrome..
....???? e or f....or neither!?
drk1980 Forum Guru
Topics: 147 Posts: 1,038
11/24/05 - 10:46 AM
#3
on second thots....
it shd be the "primary oocyte in her own germline" and not the secondary oocyte....just realised meiosis 2 wud be completed only after fertilization..
Stan Forum Senior
Topics: 16 Posts: 65
11/24/05 - 12:24 PM
#4
Thanks drk1980. I will wait for other attempts and then I'll post correct answer that I don't agree with.
Doc2378 Forum Guru
Topics: 46 Posts: 688
11/24/05 - 09:58 PM
#5
D? ___________________ Courage does not always ROAR. Sometimes courage is the quiet voice at the end of the day saying, "I will try again tomorrow" - Mary Anne Radmacher
msyamp Forum Fanatic
Topics: 60 Posts: 1,462
11/26/05 - 06:03 PM
#6
it is D. primary in her own. It cant be secondary as it is prior to invitro fertilisation
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Stan Forum Senior
Topics: 16 Posts: 65
11/27/05 - 12:58 PM
#7
I think it is a confusing question. The correct answer is F. I think theoretically D and E are also possible.
Thanks
reet Forum Fanatic
Topics: 152 Posts: 1,411
11/29/05 - 11:37 AM
#8
I THINK f .
PRIOR TO in VITRO FERTILISATION,,,ON ANALYSIS None of the DOWN SYNDROME SYMPTOMS Appear..,, SO it might be in vivo --implantation (BLASTOMERE DEFECT)
Edited by reet on 01/11/06 - 10:51 AM
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dharjma Forum Senior
Topics: 11 Posts: 182
12/21/05 - 08:57 PM
#9
since some have 2 copies and others have none answer is E?
RayBerg Forum Senior
Topics: 32 Posts: 150
12/31/05 - 03:36 AM
#10
Okay...I guess I'm just lost on this one. Aren't blastomeres formed *upon* fertilization? If so, E can't the the answer since we're talking about a scenario prior to fertilization. I still think that the answer is D. Please clarify...
reet Forum Fanatic
Topics: 152 Posts: 1,411
01/11/06 - 11:07 AM
#11
oogonia enter MEOSIS 1( dna replication)-pri oocyte forms and during OVARIAN cycle ,PRIMARY oocyte completes meiosis I -- forms sec oocyte + polar body.
as given prior invitro fertlisation test--- NORMAL..features
so nondisjuction in BLASTOMERES...i think
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msyamp Forum Fanatic
Topics: 60 Posts: 1,462
01/11/06 - 12:51 PM
#12
Hi guys. one sincere advise. donot beelive in all answers.
they can be very misleading.
IN this case answer is D. i strongly fix to myself. you can evaluate yourself. but my adise is some q banks can make mistakes. not always correct.
here is the explanation.
first of all the nondisjunction most of the times is during meiosis. 99 %
it can be during meiosis 1 or meiosis 2
if it is meiosis 1 it is half will be two copies and half will be having no copies as in this case.
if it is meiosis 2 some are having one copy each like normal
some are two copies and some are no copies.
if it is blastomere in her own germline it shud be when she is in her mothers uterus(i cannot be her child as no fetilisation yet.
here she will have mosaicism
POINT TO BE OTED IS PEOPLE WITH MOSAICISM HAVE SAME FEATURES AS DOWNS. MAY BE TO LESSER EXTENT. here there is no features of downs.
there she will be a mosaic
___________________ If you think you can You can! If you think you cant you are right again!!
sturge_weber Forum Guru
Topics: 77 Posts: 1,042
01/11/06 - 05:03 PM
#13
so u mean to say the ans is primary oocyte of her own germline...
i am still not sure
msyamp Forum Fanatic
Topics: 60 Posts: 1,462
01/11/06 - 05:16 PM
#14
yes i mean to say primary oocyte of her own germline D. ___________________ If you think you can You can! If you think you cant you are right again!!
reet Forum Fanatic
Topics: 152 Posts: 1,411
01/12/06 - 12:26 PM
#15
MY ANSWER IS== QUES presentation is not clear and goood..
___________________ Live as u were to die tommorow. Learn as if u were to live forever.
borrelia Forum Newbie
Topics: 1 Posts: 22
03/02/07 - 06:30 PM
#16
Mosaicism results from mitotic nondisjunction, so these individuals have cells with a normal chromosome numbers, and some that are aneuploid. So it cannot be during meiosis II it has to be during embryonic earliest divisions.
i think it is F
po Forum Elite
Topics: 39 Posts: 356
08/21/07 - 12:12 PM
#17
drk1980 wrote: on second thots....
it shd be the "primary oocyte in her own germline" and not the secondary oocyte....just realised meiosis 2 wud be completed only after fertilization..
