A question that has been on my mind is what is the first type of tissue that the zygote forms after conception? As far as I know, and please correct me if I'm wrong, the sperm and the egg fuse to form the (or at least the origin of) embryonics stem cells. These stem cells are then capable of differentiating into any cell type in the body. I'm guessing that it doesn't form one organ, then moves on to the next one, and so on, but rather develops all or most of the organs at a gradual rate simultaneously. But I'm just wondering if there is a starting point, e.g. the brain or the heart, on which the other organs are developed around. Does the body of the mother have any role in controlling the fetus' development? Or is all development dependent on the machinations of the newly formed zygote (I'm guessing Hox genes are heavily involved at this point)? I hope this question doesn't seem too misinformed -- I have a vague understanding of stem cells and am seeking to broaden my knowledge in the field.

AKAIK, the spinal chord and nervous system starts to develop first, then other tissues develop at the same time as each other.