The term for a change in the genetic structure of an organism is called a mutation. Mutations can occur spontaneously during DNA replication or be induced by environmental factors like radiation or chemicals. They can affect individual genes, leading to alterations in protein structure and function, and may have varying consequences ranging from neutral to harmful or beneficial effects. Some mutations contribute to evolutionary changes by providing genetic diversity for natural selection to act upon. Studying mutations is crucial for understanding genetics, evolution, and various genetic disorders.