Mammalian Sex Preselection: Flow-cytometric Sorting of X and Y Spermatozoa Based on DNA Difference

The sex of one’s offspring has occupied the imagination of mankind ever since the beginning of modern civilization. Theories abound as to how one can alter the sex of offspring. Early philosophers suggested that various body positions during intercourse could produce a child of one sex or the other. Still others suggested that parts of the male genital anatomy produced sperm specific to one particular sex. In mammals, X-chromosome-bearing sperm produce female offspring and Y-chromosome-bearing sperm produce male offspring, always in nearly equal numbers (50:50). Numerous investigations in animals have resulted in a significant body of literature on the skewing of this ratio. Claims for skewing of the sex ratio are commonplace, yet little if any verification has been offered to support them. Many of these protocols use one or more of the physical sperm measurements (size, shape, swimming speed, surface antigen, etc.) as the marker specific for X or Y sperm. A separation technique is then performed based on this “specific marker”. None of the protocols based on these proposed markers of X or Y sperm has been shown to skew the sex ratio to any extent. The reader is guided to reviews which describe many of the “physical separation methods” in more detail than is possible here (Kiddy and Hafs 1971, Amann and Seidel 1982, Gledhill 1988, Johnson 1994, 1995).