Sperm Sex Ratio (X: Y Ratio) and its Variations

Sex ratio can be studied at various levels viz., at the time of spermatogenesis i.e. ratio of X and Y bearing sperm (pre-zygotic sex ratio) or at the time of fertilization/early preimplantation embryo (close to primary sex ratio or post-zygotic sex ratio) or at the time of birth (secondary sex ratio). The natural sex ratio at the time of spermatogenesis is expected to be 1:1. In this study we have examined sex ratio in ejaculated spermatozoa (human) as well as epididymal sperm (mouse) to determine proportion of X and Y bearing sperm i.e., pre-zygotic sex ratio. We also examined effects of seasons (temperature; summer vs. winter), diet (vegetarian vs. non vegetarian), profession (professionals vs. laborer) on sperm (pre-zygotic) sex (X: Y) ratio of ejaculated sperm. The sperm sex ratio was carried out on 813066 human spermatozoa and 10390 mouse spermatozoa. In human, we have found more (52%) X than Y (48%) bearing sperms (421531X: 391535Y or 1.07X: 1Y). In mouse also we observed preponderance of X (55.5%) as compared to Y (44.5%) bearing sperms (1.24X: 1Y). In all sub-groups (season, diet, profession) we have observed more X bearing sperm. Our observations at pre-zygotic sex ratio have shown skewed sex ratio towards female. A probable reason for this could be preferential elimination of Y bearing sperm. This is also supported by the evidence of more aneuploidy with Y-bearing spermatozoa (~1.5 times more with Y bearing sperms).