Migration of human spermatozoa in cervical mucus obtained from women shortly before mid-cycle was studied, using an in-vitro method for horizontal sperm penetration. The results indicate that a small number of Y-bearing spermatozoa form the frontal zone during active migration.A deviation of sex ratio depending on the time of conception during the menstrual cycle has been postulated on the basis of clinical observations and, more recently, of differential migration of X-and Y-bearing spermatozoa (Fürst
Numerous attempts have been made to separate the X-and Y-bearing spermatozoa of mammals (Kiddy & Hafs, 1971 12,000, 26,400, 49,600, 63,600 or 77,500 g. The centrifuged tubes were photographed by indirect illumination and the densitometer tracing was made from the photographic negative. The tubes were fractionated by aspiration of the different banding regions, using a special glass pipette with a finely drawn outlet. The fractions were washed with Ca2+-free Ringer and concentrated by centrifugation. The sedimented material was suspended in drops of 0-15 M-NaCl, and slides stained with quinacrine dihydrochloride were made. These were analysed by fluorescence microscopy as described by . The first 1500 morphologically 'intact' spermatozoa were analysed in each fraction and in smears of the corresponding semen samples. In Fractions 1 and 2, only 100 to 500 cells and 500 to 1500 cells, respectively, were counted due to the lack of material.A characteristic pattern of density gradient centrifugation of human sperma-587
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