Which step reconstructs the electron density map in XRD?
Diffraction experiment records intensities yielding amplitudes of structure factors but loses phase information, known as phase problem. To recover real-space electron distribution, crystallographers apply Fourier transformation, specifically inverse Fourier synthesis of structure factors F(hkl) incorporating experimentally determined amplitudes and computationally estimated phases. Crystallization generates ordered lattice, radiation exposure creates diffraction pattern, drying is irrelevant to map generation. Phase determination via molecular replacement, anomalous dispersion or heavy-atom isomorphous replacement followed by iterative Fourier cycling and refinement reconstructs electron density where polypeptide backbone can be traced accurately for model building.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.