PSY210H5 Chapter Notes - Chapter 3: Twin, Prenatal Development, Blastocyst
Document Summary
Chapter 3: prenatal development, birth, and the newborn. The changes that transform a fertilized egg into a newborn human make up prenatal development. Prenatal development takes an average of 38 weeks, which are divided into three stages: the period of the zygote, the period of the embryo, and the period of the fetus. During these two weeks, the zygote grows rapidly through cell division and travels along the fallopian tube toward the uterus. Within hours, the zygote divides for the first time; after that, division occurs every 12 hours. Occasionally, the zygote separates into two clusters that then develop into identical twins. Fraternal twins, which are more common are created when two eggs are released at the same time and each is fertilized by a different sperm cell. While it is from the early division of the zygote that monozygotic twins arise, in rare cases the zygote may divide even more, giving rise to more identical individuals, such as triplets.
