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.
However, unlike echinoderms, chordates are characterized by a notochord, jointed appendages, and segmentation. Four features characterize the chordates and have played an important role in the evolution of the phylum: 1. A single, hollow nerve cord runs just beneath the dorsal surface of the animal.In vertebrates, the dorsal nerve cord differentiates into the brain and spinal cord.2. A flexible rod, the notochord, forms on the dorsal side of the primitive gut in the early embryo and is present at some developmental stage in all chordates.The notochord is located just below the nerve cord.n vertebrates, the dorsal nerve cord differentiates into the brain and spinal cord. 2. A flexible rod, the notochord, forms on the dorsal side of the primitive gut in the early embryo and is present at some developmental stage in all chordates. The notochord is located just below the nerve cord.