Genetics is the science that studies genes and the resulting diversity of organisms. The principles of trait inheritance have been in use since ancient times to improve agricultural yield and animal breeding by marrying animals of good breed. Genetics began at the hands of the famous scientist Mendel to study the transmission of genetic traits from parents to children and the proportions of their distribution among members of different generations. These studies now known as the science of classical genetics. But modern technologies have now allowed geneticists to investigate the mechanism of genes and know the exact sequence of amino acids within the DNA and RNA of the genetic material, and then to link this sequence with genes, and this has allowed the completion of one of the largest projects of the twentieth century: the human genome project.