We all know that the fetus lodges in the maternal womb where it grows quietly. What they may not know is that almost from the first moment their DNA is dispersed throughout the circulatory system of the mother.
Remember that gestation begins with the fusion of the gametes: the maternal ovum and the paternal sperm. The fertilization gives rise to the zygote, a giant cell that divides many times until it is a ball of cells called a morula. So far all the cells were the same, but now some go to Houston and others to California since the first cell differentiation that culminates in the blastocyst takes place.