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.
notochord noÂ·toÂ·chord (nÅ'tÉ-kÃ´rd') n. A flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive backbone. A similar structure in embryos of higher vertebrates, from which the spinal column develops.