The Fine Art of Sperm Cell Sorting

June 28, 2002

Sorting X and Y sperm for purposes of predetermining female or male offspring is, at best, a laborious process.

It takes a concentrated dose of 20 million X (female) sperm to generate a 90 percent chance of producing a milk cow through artificial insemination. For horses, 500 million sperm are required. Count on 3 billion sperm to conceive a sow using presorted sperm.

After several years of engineering and fine tuning, XY Inc. has managed to increase its sorting rate to about 5,000 X or Y sperm per second -- not a fast process for customers who require 3 billion-sperm doses.

Still, it’s a far cry from the 1,200-per-second rate in effect when XY formed in 1996 to merge and market techniques developed earlier at Lawrence Liver-more National Laboratory, the U.S. Department of Agriculture, Colorado State University and elsewhere.

Technological tweaking may speed sorting rates further. Low-dose insemination strategies -- 2 million sperm, say, instead of 20 million for a cow -- eventually will allow XY licensees to produce as many as seven doses per hour, said President Mervyn Jacobson.

Sperm sorting for gender selection is made possible by special versions of flow cytometers -- the same machines that sort cells in DNA research and other areas of scientific discovery. Cytomation Inc., a Fort Collins company in which Jacobson previously held an interest, makes XY’s MoFlo.

Because Cytomation isn’t likely to sell a MoFlo for sperm-sorting purposes unless its customer also has licensed XY sorting technology, XY has become a marketing arm of sorts for the manufacturer, Jacobson said.

Sperm first is collected from bulls or other male livestock and placed in a liquid suspension. Fluorescent dyes are then applied. The X (female) sperm is structured in a way that it absorbs 4 percent more of the dye than Y (male) sperm.

The sperm are sent in a stream past a low-energy laser. Because the X sperm express 4 percent more fluorescence, they can be sequestered from the Y sperm. A special vibration frequency allows sperm to be encased, one each, in tiny droplets that are shaken off from the stream. Negative and positive charges are applied to the droplets to redirect the sperm to separate receptacles, depending on gender. A third receptacle catches dead sperm.

In an effort to optimize sperm cell sorting rates, XY continually refigures specifications associated with the MoFlo nozzle, calibration of the instrument and other hardware issues.