The actual process of genetically modifying an organism is complicated, involving several steps. Also there are several different techniques used to take DNA from one organism and insert it into another. Often many attempts must be made before success is achieved. Even the most simple of living organism are very complex and the higher-ordered organisms such as agricultural plants and animals are tremendously complex. A gene map may contain as many as a hundred thousand genes. By far the most difficult task involved with gene splicing is that of locating the gene responsible for certain trait. Remember that genes are arranged on a chromosome in a particular sequence. Locating the proper sequence that controls a particular trait is quite literally like crying to find a needle in a haystack.
To find a particular gene responsible for a particular characteristic a scientist must locate what are called markers. Markers are generally found by comparing DNA patterns on fragments of DNA. Samples of DNA from an organism having the desired characteristic. For example, if a scientist wishes to locate the gene responsible for giving a corn plant resistance to a virus, he or she will compare a fragment of DNA from a plant having the resistance. Differences in the samples of DNA fragments are examined and noted. These differences can be used as markers to locate the desired gene. The comparison of these patterns is known as restriction analysis.
A slightly different form of restriction analysis is also used. This technique is called Restriction Fragment Length Polymorphism (RFLP). In this process, a scientist will cut fragment of DNA from tissue to be compared using an enzyme that cuts DNA at a specific site. This enzyme are called restriction enzymes. The sample fragment are then sorted by a process called electrophoresis, a method of sorting DNA fragments according to size by subjecting the fragments to a direct electric current that draws the DNA through a gel.
