Gastrulation and the formation of the three germinal layers is the beginning of the subdivision of the mass of embryonic cells produced by cleavage. The cells then begin to change and diversify under the direction of the genes. The genes brought in by the sperm exert control for the first time; during cleavage all processes seem to be under control of the maternal genes. In cases of hybridization, in which individuals from different species produce offspring, the influence of the sperm is first apparent at gastrulation: paternal characteristics may appear at this stage; or the embryo may stop developing and die if the paternal genes are incompatible with the egg (as is the case in hybridization between species distantly related). Encyclopædia Britannica, 2009.
Search under 'Gastrulation' in the article on animal development.
Sorry guy, but you clearly don’t understand what you are talking about. That only says that there is a period where maternal genes are influential and at the end of that period, paternal genes also come into play. The unique DNA of the child exists from the time fertilization is comlete. The zygote is a unique individual human being.
Once more, do feel free to provide some credible material that states explictly that the offspring of two human beings is EVER anything but a living human being.
It was nearly effortless for me to provide several credible sources that state explictly that we are indeed living human beings from the time we are concieved. In fact, one states clearly that a zygote is a unicellular human being.
By now, it should be clear to you that you are not going to find anything that suggests that unborns, even at the very early stages are something other than living human beings, but by all means, keep reaching for straws. There is a certain facination to be found in your efforts.
You are very good at describing things but not very good at explaining why they are relevant to the discussion. You need to explain why it matters, not simply what happens. Nothing that happens at "gastrulation" hasn't already been locked in place from the point at which the sperm entered the egg. That the genes are on or off or working or not is irrelevant to the status of the individual in question. The genes that are going to start working at "gastrulation" are already determined. And bear in mind that even two distinct fertilized eggs can fuse later in a pregnancy to produce a chimera -- a mosaic of two sets of cells with different genes that together form a single complete body, so it's not as if the point where the number of individuals can change isn't quite a bit after the point you are obsessing over. Of course none of this is relevant if you look at more than individual trees to see the forest.