How does agarose gel electrophoresis help complete genotype identification in animal experiments?

Why Genotyping Is Needed for Animal Experiments

In animal experiments, especially when using models such as transgenic mice and knockout rats, researchers need to confirm whether each animal carries the target gene fragment. Because animals from the same breeding batch may have different genotypes, subsequent experimental results will become difficult to interpret if they are not distinguished. Genotyping is like checking an animal's "genetic ID card," helping researchers divide animals into different groups and ensuring that the genetic backgrounds of the experimental group and the control group are clear and controllable.

This process usually starts with extracting DNA from animal tissue, then amplifying the target region by PCR, and finally observing the DNA fragments by agarose gel electrophoresis. In this step, agarose plays the role of a "sieve," allowing DNA fragments of different lengths to separate in an electric field.

How Agarose Gels "Sieve Out" DNA Fragments

Agarose is a natural polysaccharide extracted from seaweed. After heating, it can dissolve in water, and after cooling, it forms a transparent gel. The gel contains many tiny pores inside, like a three-dimensional net. DNA molecules carry a negative charge and move toward the positive electrode under the action of the electric field in the electrophoresis tank. Shorter DNA fragments pass through the pores more easily and run faster; longer fragments encounter greater resistance and run slower. After a period of time, DNA fragments of different lengths become distributed at different positions, forming individual bands.

The concentration of agarose gels commonly used in laboratories is generally between 0.8% and 2%. Low-concentration gels have larger pores and are suitable for separating longer DNA fragments; high-concentration gels have smaller pores and are suitable for separating shorter fragments. When selecting, suitable electrophoresis buffer and DNA molecular weight markers should also be used together to determine the size of sample bands.

General Workflow from Sample to Result

In genotyping of transgenic animals, a small piece of tail tip or ear margin tissue is usually first clipped, and genomic DNA is extracted. Then PCR amplification is performed with specific primers to obtain the target DNA fragment. After mixing the PCR product with loading buffer, it is added to the wells of an agarose gel, and the power supply is turned on for electrophoresis. After completion, nucleic acid dye staining is used, and the band positions are observed under ultraviolet light or blue light. If a clear band appears at the target position, and this is judged together with controls, it can be preliminarily determined whether the animal carries the target gene.

This workflow has a low operational threshold, but it requires patience and care. For example, avoid sample overflow during loading, control voltage and time, and avoid overheating of the gel. For beginners, it is recommended to first practice with samples of known genotype to become familiar with band positions and judgment criteria.

What to Pay Attention to When Selecting and Using It

The quality of agarose affects the transparency of the gel and the resolution of electrophoresis. Laboratories generally pay attention to the gel strength, purity, and residual nuclease status of agarose. When heating to dissolve, the solution needs to become completely transparent, with no undissolved particles. Cool to about 60°C before pouring the gel, which can reduce bubble formation. Before pouring the gel, confirm that the comb is in the correct position. After the gel solidifies, pull out the comb vertically to avoid damaging the wells.

In addition, gels containing nucleic acid dyes should be handled in accordance with laboratory waste management regulations and must not be discarded at will. Electrophoresis buffer needs to be replaced regularly to avoid changes in ion concentration affecting separation performance. By using agarose in a standardized way, genotyping results in animal experiments can be more stable and reliable.