The basic laws of inheritance were discovered in 1866 by Gregor Mendel. He defined the concept of a gene - the basic unit responsible for possession and passing on of a single characteristic. A period of over 75 years has passed from the time the laws of inheritance were discovered until the biological role of DNA (Deoxy-Ribonucleic acid) was elucidated. It is now known that the DNA is the major carrier of genetic material in living organisms.