Where does an organism’s DNA come from?

There are many Theories about the origin of life itself. Evolution is one, Mythological ones also exist.
But here are some facts:
IN 1953, molecular biologists James Watson and Francis Crick published a discovery that was critical to our scientific understanding of life. They had discovered the double-helical structure of DNA. * This threadlike substance—mostly found in the nucleus of cells—contains encoded, or “written,” information, making cells living libraries, as it were.

Professor Yan-Der Hsuuw, director of embryo research at Taiwan’s National Pingtung University of Science and Technology, states, regarding cell division and specialization, “The right cells must be produced in the right order and at the right places. First they assemble into tissues that will in turn assemble themselves into organs and limbs". He further says, "What engineer can even dream of writing instructions for such a process? Yet the instructions for embryo development are superbly written in DNA. When I consider the beauty of it all, I’m convinced that life was designed by God.”

The Bible writer David said in prayer to God: “Your eyes even saw me as an embryo; all its parts were written in your book.” (Psalm 139:16)
None of the Bible writers were even slightly influenced by the fanciful folklore or mythology of other ancient peoples, who believed in all sorts of stories.

Further research on this and other information about man's origin can be found on this website jw.org.