Telomerase transcription in proliferative cells

Steps:

• Telomerase adds telomeres to chromosome ends, essential for cells that divide repeatedly.
• Germ cells and stem cells require telomerase to sustain telomere length across generations or self-renewal.
• Most differentiated somatic cells repress telomerase transcription to limit proliferation.
• Thus, only cells labeled 1 (stem) and 2 (germ) actively transcribe telomerase enzyme.

Why B is correct:

• Telomerase is transcribed in cells with high replicative potential, per the end-replication problem in DNA synthesis, matching stem (1) and germ (2) cells.

Why the others are wrong:

• A includes 3, but somatic cells repress telomerase to prevent uncontrolled division.
• C excludes 2, but germ cells transcribe telomerase for gamete production.
• D excludes 1, but stem cells transcribe telomerase for tissue maintenance.

Final answer: B