In 1856 Gregor Mendel began an extensive series of experiments upon culinary peas, with the aim of determining general laws governing the development of specific traits in hybrid species. After he cross bread 22 different pea plants, and examined over 10,000. After his experiments he came up with the law of independent assortment (specific traits), the law of independent segregation (which is inherited characteristics) , and the law of dominance (one trait is dominant and the other is recessive). Then in 1869 Miescheer discovered DNA. Then in the 1950's Watson and Crick discovered the double helix which is a pair of parallel helices connected about in a common axis, especially that in the structure of the DNA molecule. https://www.youtube.com/watch?v=CmUkvqd4te8