Medical genetics is concerned with how diseases, birth defects, or other health problems are inherited or passed down from one generation to the next through the genes. Genes are the building blocks of heredity that hold DNA, the instructions for making proteins. Proteins do most of the work in cells by moving molecules to where they are needed, building structures, breaking down toxins and doing general clean up and maintenance work around the body. Sometimes there is a mutation or a change in a gene or genes. This effects the gene's instructions for making a protein. If the protein is missing or not working properly, this causes a medical condition known as a genetic disorder.