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.
And exactly why do you believe that gastrulation marks anything beyond another stage of development. You clearly don’t understand the topic and are grasping at wiki straws. Here are some references from medical school textbooks used to teach the subjects of embryology, fetology, developmental biology, and OB/Gyn and highly respected, peer reviewed medical journals. They are quite explicit with regard to when an individual human being’s life begins.
“Often,this morula is inaccurately referred to as a ‘fertilized egg’ because the blastomeres remain inside the female parent’s oocyte outer cell membrane. That is an incorrect characterization, because the 23 -chromosome oocyte no longer exists; all the cells within the morula have the unique genome—46 chromosomes and a complement of mitochondrial DNA —of the newly conceived individual life.” Moore and Persaud, The Developing Human, 6th ed., (p. 43)
“the proposition that an unborn child is a human being from conception is “supported by standard textbooks on embryology or human biology”T.W. SADLER, LANGMAN’S MEDICAL EMBRYOLOGY (John N. Gardner ed., 6th ed.
“Fertilization is an important landmark because, under ordinary circumstances, a new, genetically distinct human being is thereby formed... The zygote is a unicellular human being... Ronan R. O’Rahilly, Fabiola Muller, (New York: Wiley-Liss), 5, 55. EMBRYOLOGY & TERATOLOGY
“Every time a sperm cell and ovum unite a new human being is created which is alive and will continue to live unless its death is brought about by some specific condition.”E.L. Potter and J.M. Craig, PATHOLOGY OF THE FETUS AND THE INFANT, 3d ed. (Chicago: Year Book Medical Publishers, vii.
“Physicians, biologists, and other scientists agree that conception marks the beginning of the life of a human being—a being that is alive and is a member of the human species. There is overwhelming agreement on this point in countless medical, biological, and scientific writings.” John C. Fletcher, Mark I. Evans, “Maternal Bonding in Early Fetal Ultrasound Examinations,” New England Journal of Medicine, February 17, 1983.
Now do feel free to provide some equally credible sources that state explicitly that the offspring of two human beings is EVER anything other than a human being.