How Do They Do It?
The sexed semen process explained:
The X chromosomes (determines female) in most animals contain more genetic material than the Y chromosome. The sorting process revolves around detecting the difference.
After a sample passes an initial quality control check, it is combined with a media that nourishes and invigorates the sperm. The media also contains a fluorescent dye that binds with genetic material. The more genetic material a sperm contains the more dye it absorbs.
The sample is then put though a sorting machine called a flow cytometer. The machine arranges the sperm in single file line and then sends them past a laser. The laser hits each sperm causing the dye to fluoresce. The amount of fluorescence tells the flow cytometer whether the sperm is carrying an x or y chromosome. The cytometer then attaches a slight electric charge to the sperm based on the chromosome it is carries.
As the sperm exits the cytometer, they pass between two charged plates- one with a positive charge and one with a negative charge. The charge applied to the sperm cell and the charge of the plates combine to direct the sperm cell into the appropriate gender specific vial.
Source: Jim Hiney Sexing Technologies