Hi LeniGrey, apologies, I cross posted with you.
There are no pre-DNA stages, an egg contains DNA and a sperm contains DNA. The moment of fertilisation literally brings that DNA together to make an embryo when the sperm penetrates the egg. The DNA is in the form of sex and non- sex chromosomes.
An egg contains a single X sex chromosome (made from DNA).
A sperm contains either an X or a Y sex chromosome (made from DNA)
So a female embryo is made by a X carrying sperm (the embryo is XX) and a male embryo is made by a Y carrying sperm (the embryo is XY).