Most of these are not compatible with life. Abnormality of individual genes, including new mutations, may also cause congenital abnormalities. Many of them, however, are compatible with successful pregnancies and even normal life spans. Developmental errors, whether genetic or teratogenic, generally result from disruption of normal developmental processes and mechanisms. Developmental Mechanisms Developmental mechanisms are those processes and activities that stand behind the observable features of development, which can be used to understand both normal and abnormal development.
Growth is often different amongst different cell populations, which is then seen as relative growth.
Differentiation, especially, also involves the generation of cell diversity. These changes within a cell's lineage reflect a heirarchy of 'cellular decisions'. From generation to generation during development, individual cells lose the potential of becoming a wide variety of cell types as they become increasingly specialised. Cells of the morula, for example, are described as totipotent , because they can become cells in any part of the embryo or extraembryonic tissues. These early totipotent cells are also known as embryonic stem cells , because they are at the very stem of the cellular family tree.