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|Chapter Six: DNA, RNA, and Protein Synthesis|
Most people look somewhat like a mixture of their parents. They may have their father's nose or their mother's eyes, but in general, certain traits are passed on from one generation to the next. This is also the case with unicellular organisms. This "genetic information" (the information which determines the traits which are passed down) must be stored somewhere in the cell, but just how or where eluded biologists for a long time.
Eventually, microscopists noticed that during cell division, the sister chromatid pairs split, and each corresponding chromosome became part of a different daughter cell. This phenomenon suggested to biologists that the chromosomes must in some way contain the genetic information, especially since cells which obtained an abnormal number of chromosomes failed to function. However, chemical analysis showed that the chromosomes were made of two major components: DNA (deoxyribonucleic acid) and protein.
DNA was, at the time, thought to be a much simpler molecule than proteins, which scientists knew came in many varieties and combinations. So, it seemed logical that they hypothesized that protein was the genetic material. But by the late 1920s and 1930s, experimental evidence (discussed in the next section) began to mount that DNA was in fact the bearer of genetic information.