SELECTIVE ISOLATION OF HUMAN X-BEARING SPERM BY DIFFERENTIAL VELOCITY SEDIMENTATION IN PERCOLL DENSITY GRADIENTS

Examinations of sperm sedimentation in Percoll density gradients suggested that the sedimentation velocity of X-bearing sperm was faster than that of Y-bearing sperm, despite the fact that the apparent densities of the two types of cells obtained by equilibrium sedimentation were similar. From this, it seems difficult to obtain both types of cells simultaneously by only one procedure. Assuming that the ease with which the cells pass through the density interfaces influences their sedimentation velocity, a discontinuous density gradient with 12 steps (25 to 80% Percoll) was adopted for the selective isolation of X-bearing sperm. Among the conditions examined, centrifugation at 250 g for 30 min gave the optimum result: 23.3 ± 6.3 % of sperm was recovered in the sediment, of which the percentage of Y-bearing sperm was only 6.4 ± 1.8 %; thus the purity of X-bearing sperm was approximately 94 %. Almost all the sperm in the sediment were active and forward motile.