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Old 09-09-2012
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Zygote Monozygotic twins - when do they split?

Approximately 1 in 90 pregnancies results in twins in the United States. Knowing whether the twins are fraternal (dizygotic) or identical (monozygotic) twins is important if tissue and organ transplantation becomes necessary. Most monozygotic twins arise by splitting of the conceptus at which of the following stages?

a) Bilaminar germ disc stage
b) Blastocyst stage
c) Morula stage
d) Trilaminar germ disc stage
e) Two-cell stage

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Old 09-09-2012
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C) morula stage is my answer----75% twins divide before entering into blastocyst stage

in/after blastocyst stage ,<1% twins divide.....

at 2 cell stage 25% divide
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Old 09-09-2012
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Default Blastocyst stage

BB..division between days 4-9(blastocyst form at day 8)

Division at morula stage(day 3)forms dizygotes?
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Old 09-11-2012
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blastocysts stage division produces monozygotes or cojoint twins?
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Old 09-11-2012
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Default correct answer :)

The answer is b) Blastocyst stage - Most monozygotic twins arise by subdivision of the inner cell mass in a blastocyst -> common placenta and chorionic cavities but separate amniotic cavities.
If the splitting occurs later, eg. in the 2nd week - they have common amniotic cavities.
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