You should take your two copper coins and invest in some books on human developmental biology. The child begins to act as an individual human being within seconds after sperm entering the egg beginning with an immediate thickening of the egg wall denying entry of antoher sperm.
Your idea that conception takes 16 to 18 days brings your abject ignorance of developmental biology into sharp relief.
The child begins to act as an individual human being within seconds after sperm entering the egg beginning with an immediate thickening of the egg wall denying entry of antoher sperm.
It's a triggering mechanism from the sperm cell's acrosomal cap that causes the egg's membrane to deny entry of other sperm. The father's DNA has had no role to play at this time, and the fusion is not yet an individual (the chromosomes haven't yet paired).
http://en.wikipedia.org/wiki/Gastrulation
In mammals, gastrulation occurs after implantation, around day 16 after fertilization in human embryogenesis. As the outer cell mass invades the endometrium, the inner cell mass divides into two layers: the epiblast and hypoblast. The hypoblast spreads out and covers the blastocoel to form the yolk sac. The yolk sac is an extraembryonic tissue that produces blood cells similar to the structure that surrounds the yolk in birds. The epiblast further divides into two more layers. The amnion layer forms the fluid filled cavity to surround and protect the embryo during pregnancy. The embryonic epiblast undergoes gastrulation.
Gastrulation, which occurs around 16 days after fertilisation, is the point in development when the implanted blastocyst develops three germ layers, the endoderm, the ectoderm and the mesoderm. It is at this point that the genetic code of the father becomes fully involved in the development of the embryo. Until this point in development, twinning is possible. Additionally, interspecies hybrids survive only until gastrulation, and have no chance of development afterward.