Given the accepted tetranucleotide hypothesis, most workers assumed that deviations from equimolar base ratios were due to experimental error. Erwin Chargaff (1905 - 2002) showed experimentally that base compositions actually varied among species, however in all species the molar ratios [ A ] = [ T ] and [ C ] = [ G ], and that the ratio [C+G] / [ A+T ] was typically less than unity, with [C+G] is less abundant. These ratios are referred to as "Chargaff's Rules".
equivalences of A vs
T and C vs
G intuitively suggest some sort of pairing relationship.
Chargaff himself refused to speculate on the implications of his
empirical observations in the absence of further experimental
evidence, and regarded Watson & Crick's model building as a
scientifically unsound approach. Chargaff subsequently
denigrated molecular biology in general, and became embittered
over what he regarded as failure to acknowledge the importance
of his data.
HOMEWORK: Several generations of genetics students have said to themselves, "Two strands or three, bases inside or outside, and you have Chargaff's Rules - how long can it take?" Is this an accurate statement of the state of things at Cambridge in 1952.