Answer:
He extracted and observed DNA from white blood cells.
Explanation:
Friedrich Miescher, who is a Swedish Botanist, is the scientist who isolated for the first time. In 1869, Miescher isolated a chemical he called NUCLEIN, which is called Nucleic acid now.
He discovered this so called "NUCLEIN" substance from the nuclei of white blood cells. Nucleic acids are the DNA and RNA we know today, hence, Miescher's discovery was significant to the genetic code as he even agitated for the inclusion of his discovery into inheritance.
