You asked what's special about conception. Well, conception is the only time two sets of genetic code come together you form a human being. The DNA that is produced never existed before.
You see, sperm and egg are cells like any cell in your body in the sense that they have the same 46 chromosomes that every other cell in your body has. However, when sperm and egg are joined, they do something unique. The sperm will give 23 chromosomes and join to the egg that will give 23 of it's chromosome. Together they form a unique being of 46 chromosomes.
That is what is so special about conception, it is the earliest point that a unique being is created. There is no other genetic code needed at that point.