deoxyribonucleic acid, desoxyribonucleic acid, DNA(noun) (biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information.
But even adults don't often know what a notochord is. A notochord is a primitive beginning to the backbone. It appears in embryos as a small flexible rod made from cells from the mesoderm, which is one of the three layers of cells of embryos. Notochords are only found in the phylum chordata, a group of animals that includes humans.
Mesenchymal cells migrate from the primitive knot to form a midline cellular cord known as the notochordal process. The notochordal process grows cranially until it reaches the prechordal plate, the future site of the mouth. In this area the ectoderm is attached directly to the endoderm without intervening mesoderm.