Describe the processes of obtaining desired genes and their subsequent transfer into the cells of organisms.

In answering this question, it is important that the student outlines the steps and tools involved in the process (for learning purposes it is easier to learn the numerical steps, however, it is important the student is able to write the process in continuous prose as this is an essay question). For example: Firstly, the gene is identified using DNA probes, which are short sequences of DNA complementary to the desired gene and are usually either fluorescently or radioactively labelled. Restriction enzymes are then used to cut the gene out by cutting the DNA either side of the gene at specific recognition sequences. This produces sticky ends which are single-stranded DNA overhangs. To transfer the gene into a host organism a vector must be used. A commonly used vector is a bacterial vector, which is a circular form of DNA. The same restriction enzymes used previously are used to cut the vector to produce complementary sticky ends. DNA ligase is used to anneal the donor DNA to the vector DNA. The vectors must then be taken up by the host cells and a method which promotes this process is temperature shock. Marker genes are used to identify which cells have taken up the transformed plasmids (could go into more detail here but this is enough for the marks awarded for this question). The host will replicate the transformed DNA and produce the proteins coded for by the genes. This is a technology commonly used to produce medical substances such as insulin, which is used to treat type 1 diabetes.