Telomerase Activity in Specific Cell Types

Steps:

• Telomerase extends telomeres to allow repeated cell divisions without shortening.
• In most somatic cells, telomerase is inactive, leading to telomere loss and eventual senescence.
• Germ-line cells require high telomerase to preserve telomeres across generations.
• Differentiated or cultured somatic cells lack sustained telomerase expression.

Why D is correct:

• Germ-line cells (3) express high telomerase to maintain reproductive cell immortality, per telomere maintenance theory.

Why the others are wrong:

• A and B include 1 or 2, but somatic cells (1) and cultured cells (2) have low telomerase to limit proliferation.
• C includes only 1, but somatic cells suppress telomerase to prevent uncontrolled division.

Final answer: D