Genetic control of early mammalian development.

A large body of evidence, derived by the use of genetic variants and deleterious mutations, indicates that the mouse embryo both expresses and requires expression of the embryonic genome during the two-cell stage of development, at or shortly after the time of onset of RNA synthesis. It seems hopeful that the study of these very early stages of embryonic development will not only provide us with information about the genetic control of the developmental events occurring shortly after fertilization but, because of the nature of the mutations that are expressed in the homozygous form during this period, will tell us much about the genetic control of later stages of morphogenesis and about the mechanisms by which chromosome imbalance states produce their deleterious effects.