The Mystery of Twins: Identical vs. Fraternal

University:
McMaster University
Course:
1A03 | Biology
Academic year:

2024
Views:

0

Pages:

2
Author:

Esha Mahal

Anatomy and Physiology 1. In terms of the steps of fertilization and implantation, what is the difference between the two types of twins? IDENTICAL TWINS: Fertilization: A single egg is fertilized by a single sperm. During early development, the embryo splits into two, resulting in two genetically identical embryos. Implantation: Since at first there is only one single secondary oocyte that is fertilized, whether the two embryos share placentas and amniotic sacs depends on when the embryos split. FRATERNAL TWINS: Fertilization: Two different eggs are fertilized by two different sperm. In a typical menstrual cycle, only one egg is released from the ovaries, but in the case of fraternal twins, two secondary oocytes (or sometimes more) are released during the same cycle. Implantation: Since they come from separate eggs, they always have their own amniotic sacs and placentas 2. Based on the ultrasound which type of twins does Sara have? How did you come to this conclusion? Sara found that her twins shared an amniotic sac. This means that they cannot be fraternal twins because they did not come from separate eggs, they came from the same egg. Additionally, since the embryos shared an amniotic sac it must mean that the embryos split occurred later. This is called having monochorionic-monoamniotic twins. 3. Based on all this information, around what day in development do you think the twins first formed? Anatomy and Physiology 1 Sarah has identical twins, specifically monochorionic-monoamniotic twins, which means the embryo split occurred later. Usually late splitting happens around day 7-12. This late splitting allows for the formation of two embryos that share both the placenta and the amniotic sac (the embryo has already developed both the chorion and the amnion). If the split had occurred earlier (before 8 days), the twins would likely have had their own amniotic sacs and placentas. Anatomy and Physiology 2