=== Model: grok-4.6-direct | Task: bench:gpqa_diamond | Rep: 1 ===
=== Score: 5/5 | Wall: 84.268s | Cost: $0.026494 ===
=== Pass: True | Finish: stop | In-reasoning-only: False ===

--- JUDGE ---
gpqa_diamond

--- RESPONSE ---
The extra peaks observed only after standard PFA fixation (and lost upon addition of the protein–protein cross-linker DSG) are the classic signature of open-chromatin / “hyper-ChIPable” artefacts. These regions are preferentially fragmented and recovered after limited formaldehyde cross-linking; the more uniform and extensive cross-linking produced by the DSG+PFA combination largely eliminates the bias, so the artefactual peaks disappear. Active promoters and enhancers are precisely the genomic sites that exhibit this behaviour. True IKAROS occupancy at the same loci is expected to be retained (or even strengthened) by dual cross-linking, whereas peaks mapping to repeats, random genomic locations or long introns do not display this distinctive fixation dependence.

The answer is (A)