The History of DNA has been a long and interesting one. Some of the highlights include:

1. The Swiss biologist, Friedrich Miescher, isolated DNA from salmon sperm in 1868.

2. In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that DNA from pathogenic strains of the bacterium Pneumococcus could be transferred into nonpathogenic strains, making them (and any succeeding generations) pathogenic (Figure 4.8a).

3. Erwin Chargaff reported in 1947 that the quantitities of adenine and thymine in DNA were very close to the same value. Similarly, he observed that cytosine and guanine were also very close to equal in quantity.

4. In 1952, Alfred Hershey and Martha Chase showed T2 bacteriophage inject only DNA into cells and this is sufficient to make more T2 bacteriophage (Figure 4.8b).

5. James Watson and Francis Crick proposed the model of the double helix of DNA in 1953 (Figure 4.10 and Figure 4.11).

6. Matthew Meselson and Fanklin Stahl demonstrated in 1958 that DNA replication (see here) occurred by a semi-conservative mechanism (see here) in which a parental duplex yields two daughter duplexes. Each daughter duplex contains one strand from the original parental duplex and one newly synthesized strand, made by copying the parental strand.

7. In 1965, Marshall Nirenburg, Philip Leder, and others, identified the genetic code by which protein is made from information in DNA.

8. In 1979, an MIT team headed by Alexander Rich reported finding a left-handed, zig-zagging DNA strand that they named Z-DNA.