Molecular genetics (MG) is a branch of biology that studies the structure and function of genes at the molecular level. It also involves genetic engineering, which is defined as the direct manipulation of an organism's genome. Molecular genetics makes use of molecular biology's laboratory methods to link changes in the structure and sequence of human genes to functional changes in protein function, and so to health and disease. Molecular genetics is a branch of biology that studies how changes in DNA molecule architecture or expression show variety among organisms. Molecular geneticists frequently use genetic screens to discover the structure and/or function of genes in an organism's genome, employing an "investigative method." To link a gene sequence to a certain phenotype, researchers look for mutations in a gene or generate changes in a gene. Molecular genetics is a potent approach for linking mutations to genetic problems, which could help researchers find therapies and cures for a variety of hereditary diseases.