In 1982, Richard D. Palmiter at the University of Washington scientists created first “transgenic mouse” in collaboration with Ralph L. Brinster at the University of Pennsylvania. The introduction of foreign genes into mammalian embryos could form the basis of a powerful approach for studying gene regulation and the genetic basis of development.

The researchers took a DNA fragment containing the promoter of the mouse metallothionein-I gene and  fused it to the structural gene of rat growth hormone microinjected into the pronuclei of fertilized mouse eggs. Of 21 mice that developed from these eggs, seven carried the fusion gene and six of these grew significantly larger than their littermates. Several of these transgenic mice had extraordinarily high levels of the fusion mRNA in their liver and growth hormone in their serum. This approach has implications for studying the biological effects of growth hormone, as a way to accelerate animal growth, as a model for gigantism, as a means of correcting genetic disease, and as a method of farming valuable gene products.