. Cell heredity. Cytogenetics. 22 CELL HEREDITY 60 m^ Head 100 rriM 1000 A. FIGURE Structure of 72 bac- teriophage (from Kozloflf, in: Zirkle, A Symposium on Molecular Biology, Chicago, Copyright (1959) by the University of Chicago, p. 178). Tail fibers ,20 mjuj streptomycin resistance are all lost together; and in transformation studies these three genes exhibit linkage. Thus the parallel loss of activity by linked genes and independent loss of activity by unlinked genes, at characteristic melting out temperatures, are very fine evidence that linked genes are on the same molecule and unl
. Cell heredity. Cytogenetics. 22 CELL HEREDITY 60 m^ Head 100 rriM 1000 A. FIGURE Structure of 72 bac- teriophage (from Kozloflf, in: Zirkle, A Symposium on Molecular Biology, Chicago, Copyright (1959) by the University of Chicago, p. 178). Tail fibers ,20 mjuj streptomycin resistance are all lost together; and in transformation studies these three genes exhibit linkage. Thus the parallel loss of activity by linked genes and independent loss of activity by unlinked genes, at characteristic melting out temperatures, are very fine evidence that linked genes are on the same molecule and unlinked genes are on different molecules of DNA. Phage DNA Another system in which the DNA composition of hereditary material has been demonstrated is that of certain bacterial viruses, the T phages, which attack the bacterium, Escherichia coli. These viruses, or phages, have a complex structure composed primarily of protein and DNA (Fig. ). All of the DNA is in the head of the phage, and the tip of the tail contains a specific protein which attaches to particular receptor sites of the bacterial wall. After infection, multiplication occurs in the bacterial host cell, and a large number of progeny phages, genetically identical with the infecting one, are produced. Phages may differ from one an- other by a number of heritable properties which are transmitted to their progeny. Thus the phage carries hereditary determinants. One may then ask: Can the hereditary determinants be identified with a particular chemical constituent of the phage? This question was answered by the following Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sager, Ruth; Ryan, Francis J. (Francis Joseph), 1916-. New York, Wiley
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