up regulation and the cellular changes associated with an epithelial to mesenchymal transition), and human escs cultured on micro patterns, treated with bmp4, can generate spatial differentiation pattern similar to the arrangement of the germ layers in the human embryo. finally, using 3d embryoid body- and organoid-based techniques, small aggregates of mouse escs (embryonic organoids, or gastruloids) are able to show a number of processes of early mammalian embryo development such as symmetry-breaking, polarisation of gene expression, gastrulation-like movements, axial elongation and the generation of all three embryonic axes (anteroposterior, dorsoventral and left-right axes). in vitro fertilization occurs in a laboratory. the process of in vitro fertilization is when mature eggs are removed from the ovaries and are placed in a cultured medium where they are fertilized by sperm. in the culture the embryo will form. 14 days after fertilization the primitive streak forms. the formation of the primitive streak has been known to some countries as “human individuality." this means that the embryo is now a being itself, it is its own entity. the countries that believe this have created a 14-day rule in which it is illegal to study or experiment on a human embryo after the 14-day period in vitro. research has been conducted on the first 14 days of an embryo, but no known studies have been done after the 14 days. with the rule in place, mice embryos are used understand the development after 14 days; however, there are differences in the development between mice and humans.