Preimplantation development: biology, genetics, and mutagenesis.

After fertilization, the one-cell zygote grows to the morula stage and then the blastocyst stage prior to its implantation in the uterus. This series of events is under the control of the embryonic genome, although maternal cytoplasmic components may initially play a major role. The study of molecular biology has revealed a great deal concerning the organization and expression of the eukaryotic genome. Particular interest has been focused on the mechanism of control of gene expression. These mechanisms must ultimately control cellular differentiation and the early development of the embryo. The study of reproductive toxicology requires a sound molecular appreciation of gene expression and cell differentiation. Mutations of the genome can dramatically affect the embryo. Although repair mechanisms have evolved to compensate for these mutations, repairs are not uniformly successful and unrepaired mutations can lead to early fetal loss.