Genetic Disorders and Gene Therapy

Cell Science and Stem Cell Research

Fertilization and Embryogenesis is the process of Fusion of sperm and ovum to form Zygote. Fertilization usually takes place in oviduct. Ovum is in secondary oocyte stage during fertilization. Secondary oocyte is surrounded by two layer-zona pellucida and zona reticulate. Sperm move toward the secondary oocyte and bind to the receptor on zona pellucida. After sperm enter the oocyte, the zona pellucida become fertilization membrane preventing other sperm to enter. It is the entry of sperm that stimulate second meiotic division of Oocyte . Acrosome of sperm release proteolytic enzyme (Hyaluronidase) that digests the egg wall and then the pro-nucleuses fuse form zygote (2n). Zygote undergoes repeated cell division called cleavage. Cleavage starts as the zygote moves down from oviduct to uterus 3-5 days after fertilization, zygote develop into ball like structure of cell with central cavity; blastocyst (Blastula stage).Outer cell of blastocyst is known as trophoblastic cell while inner cell is known as embryonic cell. Trophoblastic cell secrete HCG (human chorionic gonadotropin) hormone; similar in function as LH. It Prevent degredation  of corpus luteum, therefore corpus luteum continue to secrete progesterone and oestrogen, which help continuous growth of endometrium wall causing menstruation cycle to stop.