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STAGES OF HUMAN DEVELOPMENT
I. Prenatal Stage and Birth • Prenatal development refers to the time between conception and birth and is typically divided into three major stages:
1. Germinal Stage (Weeks 1–2) • Begins at fertilization when the sperm and egg unite to form a zygote. • The zygote undergoes rapid mitotic cell division, forming a blastocyst. • The blastocyst travels down the fallopian tube and implants itself into the uterine wall. • Implantation typically occurs around day 6–10 after fertilization.
Biological Highlights: • Formation of placenta and amniotic sac begins. • High rate of natural failure: many zygotes do not successfully implant due to genetic abnormalities or uterine issues.