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Fertilized Egg
This event occurs within fertilization and occurs in the first 12 hours -
1st Hour
Fertilization -
Zygote stage begins
This occurs when the nuclear membrane of the ovum disappears and the 23 chromosome from the father and 23 chromosomes from the mother meet. The nuclei then double to make 46 chromosomes and fuse together -
12th hour
pronuclei join together -
30th hour
First round of mitosis (Clevage) -
40th hour
second round of mitosis -
Embryonic stage begins
This begins when the third cleavage occurs and forms a morula -
50th hour
Third round of mitosis -
Morula formed
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Day 6
64 cell embryo is now known as a blastocyst -
Day 8
Implantation -
Day 10
Ectopic pregnancy could occur -
Hatching
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Day 12
Disc with streak on the underside forms mesoderm -
Day 12
hCG begins to be secreted -
Day 15
First missed period -
Day 16
Neural tube forms -
Day 22
Heart begins to beat, arm and leg buds appear, yolk sac makes RBCs -
Day 35
Face plates forming -
Day 36
Cleft palate may occur -
Week 6
Muscles form, bent neck, webbed hands and feet, segmented back -
Week 7
Fingers and toes separate, eyes and ears formed -
Day 50
Genitalia begins to differentiate, eyelids fuse, amnion surrounds fetus -
Fetal stage begins
Occurs when all organs are formed -
Day 50
Amniocentesis can be performed -
Week 9
Chronic villi sampling could be performed -
Month 6
Eyes open, fat added under skin, head out of proportion to the body
