A totipotent, undifferentiated cell produced by cleavage of a fertilised egg up to the last blastula stage of early embryonic development (see figure below). It is blastomeres that are used for in-vitro fertilisation.
A set of blastomeres on Day 4 forms a morula
See Adhesion molecules, Blastula, Cleavage, Embryogenesis, Gastrulation, Morula