Changes

==History==

==History==

In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered several different proteins and an unusual [[acid]] in the [[nucleus]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 two American [[biologist]]s, [[Alfred Hershey]] and [[Martha Chase]] used experiments with bacteria to show that DNA passed [[gene|genes]] from one generation to the next.  

In the late 19th century [[Friedrich Miescher]], a Swiss [[biochemist]], discovered several different proteins and an unusual [[acid]] in the [[nucleus]] of cells. The acid was named deoxyribonucleic acid, or DNA. In 1944 two American [[biologist]]s, [[Alfred Hershey]] and [[Martha Chase]] used experiments with [[bacteria]] to show that DNA passed [[gene]]s from one generation to the next.  

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called adenine (A), thymine (T), guanine (G) and cytosine (C), plus phosphoric acid and a sugar. They also knew that there was always the same amount of A as T and of G as C in cells, but they did not know the rules that controlled the arrangement.

At that time, it was unclear how this simple molecule could hold all the complex information controlling the development of humans, animals and plants. Scientists knew it was made of four chemical bases called adenine (A), thymine (T), guanine (G) and cytosine (C), plus phosphoric acid and a sugar. They also knew that there was always the same amount of A as T and of G as C in cells, but they did not know the rules that controlled the arrangement.