Mutations result either from errors in DNA replication or from the damaging effects of mutagens, such as chemicals and radiation, which react with DNA and change the structures of individual nucleotides. All cells possess DNA-repair enzymes that attempt to minimize the number of mutations that occur
Invertebrates can have bilateral or radial symmetry, or they can be asymmetrical. Bilateral symmetry means that the animal is arranged in the same way on both sides. Radial symmetry means the body parts are arranged in a circle around a central point.
