Again, read the Didache.  Abortion was always considered a moral evil.  It was specifically condemned by Clement of Alexandria, St. Basil and others.  The main topic of debate, until modern science, was when ensoulment occured.  But that's a theological debate, not based on science.  Having no knowledge of DNA, or embryology, people have always debated abortion.  Gastrulation is a phase early in the embryonic development of most animals during which the single-layered blastula is reorganized into a trilaminar (three-layered) structure known as the gastrula. The term was invented in 1872.  Gastrulation occurs around day 15 following conception, well before a woman will know she's pregnant.  So you don't believe in abortion then?
There is no scientific basis for the notion that the "mother's DNA guides development until gastrulation."  It doesn't occur in an ovum for example.  The DNA from both parents is utilized at all stages of existence.  Science says human life begins at conception.