Genetic Analysis 279unique sequence of amino-acids, was in vague. However, it lost its power with the
introduction of the Pandora box of the “bewildering gene” [Falk, 1986]. Once it
has been determined that the sequence of DNA that is transcribed to RNA, resem-
bles only vaguely the RNA that is translated to a polypeptide, due to numerous
post-translational processes (see section 8), such a definite duality or any other
discontinuity in the evolution of the gene concept, seems unwarranted. Clearly
there is no one DNA sequence thaton its own, independently to the context of
the product’s function, can be unequivocally defined as a gene [Falk, 2000b, 2004].
5.1 The structure of DNA and deciphering of the code
The impact of Muller’s research project on genetic analysis can hardly be exagger-
ated. Muller extended his research program to deduce the physico-chemical nature
of genes from the genetic analysis of radiation-induced mutations to include the
study of chemically induced mutations. But as pointed out by Charlotte Auerbach
[1967] (see also Falk [1986, 152, ftn 72]), one of the pioneers of chemical mutagen-
esis, he failed in achieving his main object, the elucidation of the physico-chemical
nature of the gene by genetic analysis. It took chemical analysis to elucidate the
nature of the genetic material.
The history of the nature of the heredity material has been intensively docu-
mented (see, e.g., Olby [1974]). Evidence that the hereditary properties of bac-
teria could be transformed by DNA extracted from other bacteria was of little
impression on the genetic research community, not only because bacteria were still
considered by many as organisms whose biology profoundly differed from that of
higher-organisms, but primarily because the chemistry of DNA was not considered
complex enough to provide for the variability that was expected of the hereditary
material. Proteins were the only chemicals that showed enough variability and
diversity to answer the chemical expectations of genetic analysis. DNAs “boring”
repetitive structure could not be the holder of the necessarily rich genetic “infor-
mation”. In retrospect it is amazing to follow the rejections of Avery and others,
who persistently indicated that DNA was the carrier of genetic information. Even
evidence that the transforming element of bacteria is more than 99% pure de-
oxyribonucleic acid left the door open for the disbelievers (see Deichmann [2004;
Zuckerman and Lederberg [1986]).
Ironically, however, the experiment that turned the balance in convincing the
research community of the nature of the genetic material was after all, essentially
a biological experiment of bacteriophages (phages) transmitting their DNA rather
than their protein to their progeny. When theEscherichia coli bacteria were
infected with phages whose proteins were S^35 -labeled, only some of the radioactive
sulfur showed up in the progeny phages’ proteins, whereas once phages’ DNA was
labeled with P^32 , most of the radioactive phosphor of the nucleic acids showed up
in their progeny [Hershey and Chase, 1952].
Crick [1958] established on theoretical grounds that the genetic code was one
of triplet nucleotides coding for each of the twenty amino-acids (each coding