精蟲分離原理

以不同濃度之分層液(50%-60%-70%-80%-90%)分離精蟲
X精蟲較重，分離在底層80%-90%
Y精蟲較輕，分離在上層50%-60%

http://www.in-gender.com/Gender-Selection/Ericsson/Percoll.aspx

Sperm Preparation by Gradient Density Centrifugation

In this procedure, sperm is centrifuged through increasingly dense layers of a solution, on the theory that heavier X-sperm will sediment to the bottom, and lighter Y-sperm will migrate to top.

• A density medium, a liquid solution available in various thicknesses, is layered in a conical centrifuge tube, with the most dense layer at the bottom and the least dense layer at the top. In the standard procedure of preparing sperm for assisted reproduction, 2 layers are used. For gender selection, 3 to 12 layers are used.
• Diluted semen is layered on top, and centrifuged for 30 minutes.
• To conceive a girl, only the bottom layer, or "pellet", is retained, in which the heavier X-sperm have sedimented. To conceive a boy, only the top layer of the liquid "supernatant" is retained, containing the lighter Y-sperm.
• The remainder is washed and centrifuged again to remove the density medium.