2.2 Cleavagea series of mitotic divisions of fertilized egg -→anumber of smallerdaughter cells,blastomeresmorula (A solidball of12to 16blastomeres,formsaboutthreedaysafterfertilization.)BFirstcleavageTwocell stageDEMorulaFour-cell stage
2.2 Cleavage a series of mitotic divisions of fertilized egg → a number of smaller daughter cells, blastomeres → morula (A solid ball of 12 to 16 blastomeres, forms about three days after fertilization. )
Knnn1230Single cellTwo cell stageHoursHoursaaossuwa45Four cell stageMorulaHoursHours
Morula
BADE
2.3Blastocystformation2.3.1 Formation: morula → cell number个—spacesappearingblastocystB
2.3 Blastocyst formation 2.3.1 Formation: morula → cell number↑→ spaces appearing →blastocyst
2.3.2 StructureInnercellmassBlastoceleTrophoblast1)Innercellmass(orembryoblast)develops into embryo proper.2)Trophoblast: a surrounding layer offlattened cells, absorbs nutrients.3)Blastocele:a single cavity
2.3.2 Structure 1) Inner cell mass (or embryoblast): develops into embryo proper. 2) Trophoblast: a surrounding layer of flattened cells, absorbs nutrients. 3) Blastocele: a single cavity