1957
The Elementary Units of Heredity
S. BENZER
S
eymour Benzer's work changed our notion of the concept of the gene,
by demonstrating that the gene had a fine structure consisting of a linear array of subelements. At the time Benzer began his classic work, the
concept of the gene was different from what it is today. Genes were thought
to be indivisible and to be the smallest units of recombination, mutation, and
function. Genes could have different allelic states, but these alleles represented the whole gene, not parts of it. In one sense, genes were thought of as
beads on a necklace, the necklace being the chromosome. This picture of the
gene proved to be at odds with the physical structure of DNA elucidated by
Watson and Crick in 1953, which revealed the physical structure of the gene
to consist of a sequence of nucleotides. Each nucleotide should be able to
mutate and should also be the smallest unit of recombination. Benzer's work
bridged the gap between the classic view of the gene as an indivisible unit
and the physical structure of DNA. By exploiting the rII system of phage T4
and refining high-resolution genetic selection, Benzer was able to show that
the subelements in the gene could mutate and recombine with one another.
The smallest unit of mutation and recombination was now shown to be on
the order of only a few nucleotides or less, based mainly on genetic analysis.
Benzer also refined the cis-trans test for use with phage T4, and he defined
the cistron as a unit of gene function, a term and concept that were used for
many years.
Benzer developed the use of deletions in genetic crosses, which opened
up the entire field of fine structure analysis. It laid the groundwork for his
subsequent studies, which defined the concept of mutational hot spots, and
profoundly influenced work on mutagenesis for a generation.
JEFFREY H. MILLER
Reprinted from The Chemical Basis of Heredity, p. 70–93. Copyright © 1957, by Johns
Hopkins University Press.
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