Human fertilization establishes the genome of a new member of the human species ... an individual who is called a zygote at earliest age.
The first mega-cell is a totipotent stem cell because it will (can) give rise to the placenta as well as all the tissues and organs of the body at least one new individual organism will use upon exiting into the air world. When the zygote duplicates the 46 chromosome nucleus, and divides up the collection of mitochondrial grains, and separates into two distinct cells—each having a nucleus of 46 chromosomes as set from fertilization, the new conceived life has become two totipotent cells sharing the interior of the oocyte’s outer cell membrane, the zona pellucida, the original coat—two cells arising from one individual cell, each of the two capable of giving rise to a placental organ and all the other organs and tissues of an individual. The genome has not yet activated, because ‘construction tasking’ has not yet begun.
Within a few more hours, one of the two totipotent cells will divide to net three cells inside the zona pellucida. From the three stem cell stage onward, in normal reproduction, assigning of tasks for the new cell lines to come (stem cell lines) will begin, tasks such as building the placenta and building the embryo body to be used months later for survival in the air world.