MCQ Anatomy Answer 55

The correct answer is D.

Explanation:


Monozygotic twins, or identical twins, develop from a single fertilized egg that subsequently splits during either the blastomere or blastocyst stage. It is more common in the blastocyst stage at the end of the first week. This results in two inner cell masses in the same blastocyst cavity. They usually develop a common placenta and chorionic cavities but separate amniotic cavities.

Splitting in the second week usually results in shared amniotic cavities as well.
Conjoined twins (choice A), or Siamese twins, result from incomplete splitting of the embryo.

Dizygotic twins (choice B) and fraternal twins (choice C) are the same, and are the most common type of twins. They share the same genetic relatedness as do siblings of separate pregnancies. This type of twinning occurs because of simultaneous double ovulation followed by fertilization by two sperm. They each develop their own placenta and membranes.

A single gestation (choice E), and a single birth, is the result of a single fertilization without any splitting of the embryo.

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