The structure that joins the two strands of a chromosome together is the?

1. Analyze the question The question asks which structure holds the two strands of a chromosome together. Those "strands" are the two sister chromatids of a replicated chromosome.

2. Explain the concept Before cell division, DNA replicates. Each chromosome then consists of two identical copies called sister chromatids. These are held together at a single constricted region called the centromere. The centromere is also where spindle fibres attach during mitosis and meiosis, so the chromatids can be pulled apart to opposite poles of the cell.

3. Go through the options

• A. Spindle: This is a set of microtubule fibres that pulls chromosomes or chromatids apart during division. It does not join the strands together.
• B. Cellulose: This is a carbohydrate that makes up plant cell walls. It has nothing to do with chromosome structure.
• C. Centromere: This is the point where the two sister chromatids are joined. ✔
• D. Chromatid: This is one of the strands itself, not the structure that joins them.

4. Answer The correct option is C. centromere.

5. Exam tip Remember: Centro-mere = the "centre" joint. The chromatids are the "arms", and the centromere is the "waist" that joins them. If a question asks what the spindle fibres attach to, the answer is also the centromere.