178 
Monitoring Stem Cell Research 
Table 1: Summary of Developmental Timecourse 
Stage 
Week after 
fertilization 
Days after 
fertilization 
Event 
Pregenesis: 
develop- 
ment of 
parents 
4^^ week 
develop- 
ment of 
parents 
24 
Parents’ primordial germ 
cells (PGCs) begin their 
migration to parents’ 
gonads 
Blasto- 
genesis 
week, 
embryo is 
unilaminar 
1 
Fertilization 
1.5-3 
1®' cleavages, move to 
uterus 
4 
Free blastocyst in uterus 
5-6 
Hatching, start implantation 
2““ week, 
embryo is 
bilaminar 
7-12 
Fully implanted 
13 
Primary stem villi and 
primitive streak appear 
3""^ week, 
embryo is 
trilaminar 
16 
Gastrulation begins, 
notochord forms 
18 
Primitive pit, neural plate, 
neural groove 
20 
First somites, primitive 
heart tube 
4^ week 
22 
Neural folds fuse, 
pulmonary primordium, 
24 
PGCs begin migration. 
Cranial neuropore closes, 
optic vesicles and pit form 
26 
Caudal neuropore closes, 
arm limb buds 
28 
Leg limb buds, more brain, 
eye/ear devel. 
Organo- 
genesis 
5th _ 0th 
weeks 
29-56 
Pheno- 
genesis 
gth _ 30 th 
weeks 
PRE-PUBLICATION VERSION 
