Supersize My Mouse

Although human beings have been altering genomes by selection and breeding of particular animal or plant variants for thousands of years, and X-rays and chemicals were first used to create mutants in the early 20th century genetic engineering in the true sense only became possible much more recently. First, the discovery that genes are made of DNA, revealed the material nature of the genome. Second, scientists in the early 1970s discovered enzymes in bacteria that can be used to cut and paste DNA in the test tube. Using such molecular ‘tools‘ bacteria were engineered to produce important medical products such as human insulin for diabetics, and from this was born what would become a billion-dollar biotechnology industry. A further important development was the discovery of embryonic stem cells and manipulation of these to make ‘knockout’ mice that had a deletion of a specific gene, or ‘knockin’ mice that had subtle changes in a gene. However such an approach was still relatively expensive and time-consuming, and cold only be applied to mice. And although gene constructs could be introduced into cells in a less precise manner, the crude nature of this approach limited its application for both agriculture and gene therapy. In both areas of application there have been concerns about the safety and ethics of using such an approach. A major criticism has been the lack of precision in where a gene construct would end up the genome, leading to concerns about possible adverse effects.