This review summarizes the results of research on gene transfer to the mammalian genital tract. Gene transfer experiments have been developed during the last 2 decades and have been applied using in vitro, ex vivo and in vivo procedures. (i) In vitro methods have been applied to the uterine epithelial cells with the principal purpose of analysing some pathological change occurring in the uterus. In the male tract, epididymal cell lines have been used to evaluate the expression of particular genes and the function of specific proteins. (ii) Ex vivo methods have been applied to both the uterus and the vas deferens in humans, and good transgene expression has been recorded. (iii) In vivo gene transfer in the female tract has been employed in the uterus and oviduct using gene injections or electroporation methods. The glandular epithelium of both organs can be transfected efficiently, and transfection efficiency depends on the hormonal stage of the animal. The best expression occurred during pseudopregnancy and meta-estrus periods, when high progesterone and low estradiol concentrations occur. In the male tract, in vivo methods have been applied to mouse vas deferens and epididymis. In both organs, patches of epithelial regions appeared to express the transgenes. Furthermore, the secretions of both organs were also modified using gene constructions that led to the expression of some secretory proteins. In summary, gene modifications in the epithelium of the mammalian reproductive tract have been successful employing different technologies. Further improvements in transfection efficiency would help provide new insights into the physiology of these reproductive organs. Furthermore, the use of these methods could also be used to modify the fertility of mammals.

Sperm competition is widespread, resulting in sexual selection when the gametes of two or more males compete for access to a given set of ova. This study shows, for the first time, that sexual selection has influenced the evolution of the mammalian vas deferens – that is, the muscular duct which rapidly transports spermatozoa from the cauda epididymis to the ampulla during sexual activity. Morphometric studies of 103 species, representing 70 genera of mammals, show that the vas deferens is on average 33% shorter and its muscular walls are 45% thicker, in those forms where sperm competition pressures are greatest. The outer and inner longitudinal muscle layers of the vas are thickened under these conditions, whereas the central, circular muscle layer is significantly reduced. Thus, mammals that have multiple partner mating systems, and large testes in relation to body weight, have shorter and more muscular vasa deferentia than mammals where single partner mating systems, and smaller relative testes sizes, are the norm. These differences are statistically significant after application of procedures to correct for possible phylogenetic biases in the data set. Sperm competition has played an important role in the evolution of the mammalian vasa deferentia, favouring muscular specializations that enhance sperm transport.