Final answer:
Rosalind Franklin's X-ray diffraction data predicted that the DNA double helix contains 10 base-pairs per turn, a critical piece of information that contributed to the understanding of DNA's double helix structure revealed by Watson and Crick.
Step-by-step explanation:
The X-ray diffraction data collected by Rosalind Franklin predicted that the DNA double helix contains 10 base-pairs per complete turn of the helix. Detailed analyses of X-ray diffraction patterns and Rosalind Franklin's meticulous work, along with Watson and Crick's model building, contributed significantly to confirming the DNA structure. Each base pair is separated from the next by a distinct distance of 0.34 nm, with a full turn of the helix stretching to 3.4 nm. This 10-fold relationship between base pair spacing and helix turn pitch was critical to the understanding of DNA's secondary structure. Watson and Crick thus inferred that DNA consists of two antiparallel strands twisted into a double helix, with the uniform diameter of 2.0 nm maintained throughout due to complementary pairing between purines and pyrimidines.