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Begins to exist when the sperm reaches the egg and penetrates into the zona pellucida.
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Fertilization
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Pronuclei join together
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Occurs when the nuclear membrane of the ovum disappears and each of the 23 chromosomes from the egg and sperm combine making 23 chromosomes. The cell is ready to begin dividing.
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First round of mitosis {cleavage}
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Second round of mitosis
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Third round of mitosis
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The morula is the result of the third cleavage.
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Occurs when the fertilized egg has divided into the morula, and before it becomes a blastocyst.
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64 cell embryo {blastocyst}
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The blastocyst hatches from the zona pellucida
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Implantation
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Ectopic pregnancy could occur
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Disc with streak on the underside forms mesoderm
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hCG begins to be secreted
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First missed period
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Neural tube forms
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Heart begins to beat, arm & leg buds appear, yolk sac makes red blood cells
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Face plates forming
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Cleft lip or palate may occur
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Muscles form, bent neck, webbed hands and feet, segmented back
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Occurs when all the organs have formed the the genitalia are ready to differentiate.
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Fingers & toes separate, eyes & ears formed
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Genitalia begins to differentiate, eyelids fuse, amnion surrounds fetus
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Chorionic villi sampling could be performed
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Amniocentesis could be performed
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Eyes open, fat added under skin, head out of proportion to the body
