What is an uncondensed chromosome?

• A. Long thin strands that cannot be seen under a light microscope
• B. A chromosome after replication
• C. A circular chromosome
• D. Short, thick structures visible under light microscope

Answer: (A)

Uncondensed chromosomes are the threadlike, loosely packed form of DNA called chromatin found during interphase. In this state the DNA is long and thin, wrapped around histones but not folded into tight rods, so the strands are too diffuse to be seen with a standard light microscope. When a cell prepares to divide, the chromatin condenses into compact, thick chromosomes that are visible under light microscopy as distinct structures. After DNA replication, the chromosomes may appear as two sister chromatids still held together, but they are already compacted. The other descriptions describe condensed chromosomes (visible and thick) or bacterial circular chromosomes, which are not what uncondensed chromosomes are.