Genetics

About this course

Friedrich Miescher first observed DNA in the late 1800s, but for decades most scientists thought it too simple to carry hereditary information and expected proteins to do the job. In 1953 the work of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin showed it is a double helix. Franklin's X-ray diffraction images were the key data that Watson and Crick used to build their model. Watson, Crick and Wilkins received the Nobel Prize in 1962; Franklin had died in 1958, and the prize is not awarded after death.

The seven units go from the molecule to the tools. Genes and DNA come first: one human cell holds about 3 billion bases, and only about 1 percent of them spell out proteins. Base pairs follow, where each step of the ladder rises 0.34 nm and ten steps make a 3.4 nm turn. Chromosomes explain how about 2 meters of DNA fit in a cell. Then Mendel: in 1865 he reported crosses of nearly 30,000 pea plants, but almost nobody took notice until other scientists rediscovered his work in 1900. Punnett squares predict that two Yy plants give green seeds one time in four. Mutations show that changing one A to a T in the 20th base of the beta-globin gene gives the variant behind sickle cell disease, and DNA technology notes that 30 rounds of PCR make about a billion copies. The 3D DNA model lets you turn the helix, unzip it and watch it copy. A second lab sets up crosses of Vv × Vv plants.

This is general information, not medical or genetic-counselling advice.