Transgenic eukaryotes

DNA is introduced into a eukaryotic cell by a variety of techniques, such as transformation, injection, viral infection, or bombardment with DNA-coated tungsten particles As we learned in , when exogenously added DNA that is originally from that organism inserts into the genome, it can either replace the resident gene or insert ectopically. If the DNA is a transgene from another species, it inserts ectopically. (Vectors that replicate autonomously in eukaryotic cells are rare; so, in most cases, chromosomal integration is the route followed.)
The possibility of transgenic modification of eukaryotes such as plants and animals (including humans) opens up many new approaches to research because genotypes can be genetically engineered to make them suitable for some specific experiment. (An example in basic research is in the use of reporter genes. Sometimes it is difficult to detect the activity of a particular gene in the tissue where it normally functions. This problem can be circumvented by splicing the promoter of the gene in question to the coding region of a gene, known as a reporter gene, whose product is easily detectable. Wherever and whenever the gene in question is active, the reporter gene will announce that activity in the appropriate tissue.

Furthermore, because plants, animals, and fungi form the basis for a large part of the economy, transgenic “designer” genotypes are finding extensive use in applied research. A particularly exciting application of transgenesis is in human gene therapy—the introduction of a normally functional transgene that can replace or compensate for a resident malfunctioning allele.