human reproduction notes written by neet topper

Human sexual reproduction, to produce offspring, begins with fertilization. Successful reproduction typically involves sexual intercourse between a healthy, sexually mature and fertile male and female.[1] During sexual intercourse, sperm cells are ejaculated into the vagina through the penis, resulting in fertilization of an ovum to form a zygote.[1] While normal cells contain 46 chromosomes (23 pairs), gamete cells contain only half that number, and it is when these two cells merge into one combined zygote cell that genetic recombination occurs.[2] The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 38-week gestation period[a] for the embryo (and eventually foetus) that is followed by childbirth.