Freezing and thawing of sorted sperm was done as
described [8], but only in experiment IV. Approximately
5 106 bulk (both X- and Y-bearing sperm) sorted sperm
were collected into tubes containing catch fluid composed
of TRIS buffer with egg yolk [8]. Collection tubes were
placed in a cold room at 5 C for at least 90 minutes before
addition of an equal amount of TRIS buffer with 12%
glycerol added in two aliquots, 15 minutes apart (final
concentration, 6% glycerol). After addition of the second
aliquot, tubes were centrifuged for 20 minutes at 850 g.
The supernatant, composed of the accumulated fluids of
seminal plasma, TALP, catch fluid, and sheath fluid was
decanted, and sperm concentration of the remaining pellet
was determined using a nucleocounter. TRIS buffer with 6%
glycerol and 20% egg yolk was then added to create a final
sperm concentration of 107 sperm per mL for packaging
into 0.25 mL straws. Straws were placed on racks in liquid
nitrogen vapor (120 C) for 25 minutes, and then plunged
into liquid nitrogen (196 C) for storage. The total time
sperm were at 5 C before freezing ranged from 3 to
4 hours.