How and why scientists sequence a gene

How do scientists study DNA sequencing in genes?

Gene sequencing using radio-labeled DNA
• Reading the bases
• The Human Genome Project

Gene Sequencing

Hui-Ren, one of the scientists on Dr. Shih’s team, is sequencing the gene for MAO A by using a radiolabel. Radio-labeling allows for the sample of the gene to be exposed onto x-ray film for detection. This technique requires a glass shield to protect her from the harmful effects of radiation.

Hui-Ren loads the sample of DNA that she is studying into a polyacrylaminde gel, using a pipette.

The technique of electrophoresis ,that we see here, will pull apart the base pairs of DNA according to size. Electrophoreis is the process by which molecules (such as proteins or DNA fragments) can be separated according to size and electrical charge, through the application of an electric current. The current forces the molecules through pores in a thin layer of gel, a firm jelly-like substance called a polyacrylaminde gel. The gel can be made so that its pores are just the right dimensions for separating molecules within a specific range of sizes and shapes. Smaller fragments usually travel further than large ones. This process is also called gel electrophoresis.

The plate is removed from the electrophoresis apparatus and washed in the sink to remove the excess buffer that fills the chamber where the electric current is run through the gel.

The plates are separated in order to attach the polyacrylamide gel (which contains the radiolabeled DNA) to a filter paper. An x-ray sensitive film will be overlaid onto the gel and then exposed over night. Then our researcher will be able to see the order of bases in the DNA sequence.