BIOL-UA 12 Lecture Notes - Lecture 16: Trophoblast, Ures, Ung County
31 May 2016
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Document Summary
Splitting of the embryo during early development results in genetically identical twins, yet release and fertilization of two different eggs is what results in fraternal twins. (monozygotic; identical; mz) (dizygotic, genetically distant; dz) If mz, the twins would share some of the resources via the placenta i. e share the placenta. If dz, there are two different placenta formed: morphogenesis: After cleavage, the rate of cell division slows down and the normal cell cycle is restored. Morphogenesis is the process by which cells occupy their appropriate locations, involving: Gastrulation: rearrangement of the cells of a blastula into a three-layered embryo, called a gastrula. Where certain cells are on the blastula determines where the organs will form. Formation of the ectoderm, mesoderm and the endoderm. Blastulation is quick, but gastrulation is slowing down. During blastulation, no g phases; just m and s phases. Three layers in a gastrula are called embryonic germ layers.
