Deoxyribonucleic acid (DNA) is sometimes called the molecule of life and is found in nearly all organisms. A gene is a length of DNA that serves as the basic physical and functional unit of heredity. Genes are fundamentally instructions for the assembly of molecules called proteins, which are involved in structure and function in the human body. In this lecture, we will journey into the field of modern genetics, exploring exactly what genes do and don't do. We will consider the role of genes in diseases such as cancer, Alzheimer's disease and schizophrenia. We will be highly critical of theorists who propose that there might be a 'criminal gene' or a 'gay gene', demonstrating why this cannot be the case, and will challenge some of the theories of evolutionary psychology, particularly with regard to development of mind and brain. We will also move beyond the genome and mutational theories of disease, exploring the gene-environment interactions of epigenetics.