Fatal flaws in the case for prepatterning in the mouse egg.

The presence or absence of predetermination and polarity in the mouse preimplantation embryo is still controversial. The question is if the mechanisms underlying early mammalian development is comparable to those operating in non-mammalian 'model' organisms. In a recent article by Gardner in this journal, the author criticizes two of our recent publications. However, in order to resolve this controversy it is essential to read relevant reports carefully without bias and to provide data on which a particular claim is based.