This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Introduction, Subject name: Pathology
In-situ DNA nick end labeling can quantitate: 
Select and explain. 
A. Fraction of cells in apoptotic pathways, B. Fraction of cells in S phase, C. p53 gene product, D. bcr/abl gene
A: Fraction of cells in apoptotic pathways
Answer: A: Fraction of cells in apoptotic pathways 
Explanation: In situ DNA nick end - labeling In-situ method for detecting areas of DNA which are nicked during apoptosis. Terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) is a method for detecting apoptotic cells that exhibit DNA fragmentation.