Spermatozoal differences
Sex pre-selection is based on identifying differences between X- and Y-bearing sperm. The X chromosome contains about 4% more DNA in cattle and horses than the Y chromosome. Therefore, this difference in DNA content can be used to distinguish and select X from Y bearing sperm.

Hydrodynamic orientation
Flow cytometric sorting of mammalian spermatozoa based on DNA content is different than the process for other cell types. DNA contained within spermatozoa of mammalian animals is uniquely compact, resulting in a flat, paddle-shaped head in most species. When the DNA of sperm is stained with a harmless fluorescent dye and subjected to flow cytometry, a brighter fluorescence is emitted from the edge of the spermatozoal head compared to the more transparent flat side. Therefore, proper sperm head orientation during cytometric evaluation is critical so differences in DNA content can be evaluated correctly. Proper sperm orientation can be controlled during flow cytometric sorting using a beveled nozzle, or specially designed nozzles. The concept of sperm orientation is specifically protected under the Johnson patent, held by the USDA and licensed to XY Inc.

Given the sperm cell's unique characteristics, DakoCytomation and XY Inc. jointly are developing a new generation of flow cytometers specifically for sperm sorting. XY Inc. will have exclusive rights to this new technology for all sperm sorting applications in non-human mammals.