Nexia's "spider goat" is an example of transgenic bioengineering, that is, the introduction of DNA into a biologically unrelated creature. In this case, Nexia engineers drew on earlier work by scientists at the University of Wyoming who had located several genes that coded for the production of silk proteins in the orb weaver spider.
Nexia engineers made copies of one of those genes, and treated the gene in such a way that it could be expressed in the goat’s milk. They then inserted the gene into the egg cells of Nigerian dwarf goats. In a very small number of cases -- about 5% of the time -- the spider silk protein gene was successfully integrated into the goat genome.