Humans and rodents differ in how they carry out X inactivation (XI), the mammalian method to compensate for the different number of X chromosomes in males and females. Evolutionary changes in staging embryogenesis and in mutations within the XI center alter the process among mammals. The mouse model of XI is predicated on X counting and subsequently choosing the X to ‘inactivate’. However, new evidence suggests that humans initiate XI by protecting one X in both sexes from inactivation by XIST, the noncoding RNA that silences the inactive X. This opinion article explores the question of how the active X is protected from silencing by its own Xist locus, and the possibility of different solutions for mouse and human.

人类和啮齿动物在进行X灭活（XI）的方式上有所不同，X灭活是哺乳动物在雄性和雌性中补偿不同数量X染色体的方法。分期胚胎发生和XI中心突变的进化变化改变了哺乳动物之间的过程。XI的鼠标模型基于X计数，然后选择X使其“灭活”。然而，新的证据表明，人类通过保护两个性别中的一个X免受XIST的灭活而启动XI，XIST是使非活性X沉默的非编码RNA。这篇观点文章探讨了如何保护活性X不受自身Xist基因座沉默的问题。，以及为老鼠和人类提供不同解决方案的可能性。