In the 19th century, scientists observed mitosis and meiosis. At Columbia University, Thomas Hunt Morgan, his students, and scads of fruit flies tracked the genetic path of single-trait mutations supporting the idea that specific desirable traits could be manipulated through selective breeding.
Children often resemble their parents, but the mechanics of heredity were not well understood until the 1860s when statistician/scientist Gregor Mendel identified all the basic laws of inheritance, including the revolutionary notion that there is a double set of genetic instructions.
Follow the quest of scientists as they first delve into the level of chromosomes, then to the level of genes, and finally to DNA. In the 1940s, scientists showed that only DNA could be the genetic blueprint. It took a true flash of inspiration for Watson and Crick to come up with a form for the now famous double-helix structure of DNA that would fit all the requirements.
In the 1960s, Nirenberg cracked the genetic code by building RNA strings and correlating them with the resulting amino acid strings. The code is common to all living organisms, which made the insertion of a foreign gene theoretically possible. In the 1970s, scientists learned how to manipulate and copy DNA.
Examine the profound effects of the DNA-based revolution in agriculture. A dramatic example is the transfer of genes from one mammalian species to another, yielding modern medical miracles. A broader (and more controversial) movement into foods which have been genetically modified is compared with traditional cross-breeding methods.