Biology 1201A Lecture Notes - Lecture 18: Invagination, Umbilical Cord, Blastocyst
2 Oct 2016
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Four stages in growth and development of animal: gametogenesis (sperm/egg), embryonic development (fertilization of egg until birth), reproductive maturity (puberty), aging process to death. In mammals, development is two stages embryonic followed by fetal development. Fetus is an embryo that resembles the infant form. Stages of embryonic development (sea urchin-echinoderm): fertilization: sperm penetrate plasma membrane of 2nd oocyte. Recognition: sperm secretes proteins that bind with receptor that reside on glycoprotein layer (vitelline layer-zone pellucida in human) surrounding plasma membrane of oocyte ensures same species. Penetration: plasma membranes of sperm and oocyte fuse, sperm nucleus enter oocyte. Formation of fertilization membrane: vitelline layer forms fertilization membrane blocks additional sperm. Completion of meiosis ii in 2 nd oocyte: ovum + polar body (discharged through plasma membrane). Fusion of nuclei and replication of dna: sperm and ovum nuclei fuse zygote (diploid-23 pairs in human): cleavage: rapid cell divisions without cell growth; each cell = blastomere (less cytoplasm than original zygote)
