As we know it, our molecular life as individuals starts with a fusion between a female oocyte and a male sperm cell. When our mother was born, she got already in her ovary that small not-matured oocyte that than contributed to our first half cell at the time of ovulation many years later. Conversely, it is believed that our father just donated our second half cell by means of a sperm cell (randomly) produced de novo slight before the time of conception.
Now, Zhuoru Wu and her colleagues at the University of Texas Southwestern Medical Center in Dallas shows that when stem cells in the rat testes are at developmental crossroad, they have two choices: procrastinate becoming again stem cells or differentiate into sperm. The researchers found that when grown in the same culture medium, stem cells gave rise to more stem cells that sperm. Thus, if we want for a while being fascinated by predestination, it is conceptually possible that both the female oocyte and the male stem-to-sperm cell that initiated our life were waiting each other from the very beginning of our parent's life.
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Wu, Z., Luby-Phelps, K., Bugde, A., Molyneux, L., Denard, B., Li, W., Suel, G., & Garbers, D. (2009). Capacity for stochastic self-renewal and differentiation in mammalian spermatogonial stem cells The Journal of Cell Biology, 187 (4), 513-524 DOI: 10.1083/jcb.200907047