Abstract: Methods to introduce genetic material, such as DNA, to embryos, are disclosed. In some embodiments, the method involves preparing the pregnant mother to receive the genetic material into a blood transport vessel which passes to the embryo, avoiding a maternal capillary bed and introducing the material under low pressure so as not to kill the pregnant animal. The effectiveness of the method is such that the nucleic acid has been expressed in all the cells of the embryo and in the postnatal mouse, including the primordial germ cells, thus making the nucleic acid germ line heritable.