To make changes in the DNA, scientists employ the tools and techniques in molecular biology, particularly in genetic engineering. The first step that they do is extracting the DNA from the cells, cutting it into smaller pieces and separating it into fragments. Then, they will identify and read the order of the bases for them to be able to change its sequence. They will proceed to assemble the new sequence by cutting and pasting the genes. After this, they can now make copies of the new DNA.

Scientists identify and read the order of the bases for them to be able to determine the functions of each genes so they would know which ones should be changed or not. This allows them to form different gene combinations which creates gene variation in species.

Gel electrophoresis is a technique that is used to separate multiple fragments of DNA based on their molecular size. It is often used in detecting the presence of specific DNA sequences.

The principle behind gel electrophoresis is based on the fact that DNA molecules are negatively charged due to their phosphate groups. A mixture of DNA fragments is first loaded into a porous gel such as agarose.

The DNA mixture is then subjected to an electric current, which causes the fragments to migrate towards the positive pole of the current. Due to the small pore sizes of the gel, larger DNA fragments tend to migrate slower than smaller fragments.

The end result of gel electrophoresis would be varying bands of DNA fragments that can be visualized using methods such as UV radiation or chemical dyes. These bands are arranged based on the molecular size of the DNA fragments in the initial mixture.

A technique that can be used to make multiple copies of a gene is the polymerase chain reaction (PCR). This method makes use of specific primers and a heat-resistant DNA polymerase in order to replicate a specific sequence (gene) of DNA.

Polymerase chain reaction generally consists of three major steps. The first step is *denaturation*, wherein the DNA sample is subjected to high temperature. This causes the DNA strands to separate, which allows them to be used as a template.

The next step of PCR is *annealing*, which occurs at a lower temperature that allows for the binding of selected primers onto the separate DNA template strands. This is important to initiate the DNA replication process.

Lastly, the third step of PCR is *extension*, which involves the activity of the heat-resistant DNA polymerase. This polymerase is used to incorporate nucleotides into the new DNA strands as they are synthesized, which results in the copying of the original DNA gene.

In genetics, the genetic code is used by the genes in order to carry out special instructions, while a computer program contains sets of codes that deliver special functions. This principle of genetic engineering is similar to the way a computer programmer manipulates the codes in a particular computer program. Manipulating the DNA is like when a programmer modifies a program. He will start by getting the program out of the computer, manipulating or modifying it, and then returning it back to the computer.