This happens early in development when an embryo with two X chromosomes is just a ball of cells.

这种现象发生在胚胎发育初期，当时拥有两X体的胚胎还只是一团细胞。

But they are meant to be complete enough to provide information about what might be going on in the embryo during a pregnancy.

但它们应该足够完整，以提供有关怀孕期胚胎中可能发生的情况的信息。

Raquel says that while the essential processes involved in early embryogenesis are similar across mammalian species, the pattern of endogenous retrovirus sequences isn't.

拉奎尔指出，尽管早期胚胎发生过程中涉及的基本过程在哺乳动物物种，但内源性逆转录病毒序列的分布模式却各不同。

The IVF clinic has apologised for the accident, which is believed to be the first time that a baby has been born after the wrong embryo has been implanted in a woman.

这家体外受精诊所已就这起事故道歉。据信这是首次发生胚胎移植错误后婴儿仍得以降生的事件。