The development (starting in the 1970's) of the ability to "clone" specific pieces of DNA raised the possibilities of various kinds of applications: (1) synthesizing useful proteins from cloned genes in prokaryotic or eukaryotic cell cultures; (2) being able to engineer in a specific way the inheritable genotype of plants and animals; and (3) being able to treat genetic diseases by inserting a "good allele" into a person who has two "bad alleles" of some specific gene. The first application has been a reality now for two decades (for example, the Hepatitis B vaccine you have received consists of a protein made from a cloned viral gene.). The second application is also a reality, both in research and in agriculture. The third type of application, called "gene therapy", has been much slower to develop (due partly to safety issues) but should become a major aspect of medical biotechnology in the foreseeable future.
1. How can a gene-size or larger segment of DNA from any species be "cloned" into E. coli for the eventual purpose of large-scale production of the protein?
Figure 12.4 shows the general process. Where does the "DNA fragment from any organism" come from? It could be from (i) a restriction enzyme digestion of genomic DNA, or (ii) the results of an in vitro polymerase chain reaction amplification of a particular DNA region, or (iii) "cDNA" made in vitro by reverse transcriptase action on mRNA.
The plasmid used to clone a "several thousand base pairs" fragment of DNA must have specific properties that allow for insertion of the foreign DNA and selection for transformed bacteria that have taken up the plasmid containing the foreign DNA. An example of such a plasmid cloning vector, and how it works, is shown in Figures 12.9 and 12.10. This plasmid and process is almost identical to what you will be doing in the BioS 116 lab experiment "Cloning in E. coli".
2. What is a late 2005 update on mammalian transgenics?
On September 23, 2005, the journal Science published a major research advance titled "An Aneuploid Mouse Strain Carrying Human Chromosome 21 with Down Syndrome Phenotypes ". Let's take a look at this research article to get a sense of what the frontier is in this field. (Journal access reminder: You must access this article through a Lehigh web connection, so the journal Science "sees" that you have a subscription.)