胚胎的性别早在受精时就决定了。

The sex of the embryo is predetermined at fertilization.

《牛津词典》

她第一次接受体外受精时，那还是一个比较新的方法。

When she first underwent IVF it was still a relatively new procedure.

《柯林斯英汉双解大词典》

当卵子受精时，这些物质变得活跃起来，并可能控制与它们相互作用的基因的行为。

When the egg is fertilized, the substances become active and, presumably, govern the behavior of the genes they interact with.

youdao

So on the personality theory, I did not exist when that fertilized egg came into being, when the egg and the sperm joined.

所以在人格理论上，卵子受精的时候我还不存在，卵子和精子结合时。

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