Generation of Transgenic Livestock by Pronuclear Injection

The first transgenic livestock were reported in 1985 (1 ). The techniques for producing these animals used pronuclear injection, which had been established previously in the mouse (2 ). This technique involves the direct introduction of a few hundred copies of a DNA construct into one of the two pronuclei of the fertilized egg. The injected DNA concantenates, generating tandem arrays, which integrate at what are assumed to be random sites in the genome in a small proportion of injected eggs. In mice, typically 10-20% of the pups that are born will carry the foreign DNA, and the majority of these founders will transmit the new DNA sequence to the next generation (3 ).