Chromosome must condense to approximately 1/500th of their length for cell division. The first reduction is

Options

A. coiling around nucleosomes
B. looping of solenoid fibres to form 300 nm fibres
C. forming of coiled solenoid fibre
D. looping of 300 nm fibre

Explanation

To answer the question regarding the first reduction of chromosome length during cell division, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding Chromosomes**:
- Chromosomes are structures within cells that contain DNA, which carries genetic information. They are usually long and thread-like.

2. **Need for Condensation**:
- During cell division, chromosomes must condense to fit within the cell. They need to become much shorter and more compact to ensure that they can be evenly distributed to daughter cells.

3. **First Reduction - Coiling**:
- The first reduction in the length of chromosomes occurs through a process called coiling. This involves the DNA wrapping around histone proteins to form a structure known as a nucleosome.

4. **Formation of Nucleosomes**:
- Each nucleosome consists of a segment of DNA wrapped around a core of histone proteins. This structure resembles "beads on a string," where the beads are the nucleosomes.

5. **Further Coiling into Chromatin**:
- The nucleosomes further coil and fold to form a more compact structure known as chromatin. This chromatin can then loop and coil further to form the condensed chromosome structure.

6. **Final Structure**:
- Ultimately, through these processes of coiling and looping, the chromosomes condense to about 1/500th of their original length, making them ready for cell division.

### Conclusion:
The first reduction in chromosome length occurs through the coiling of DNA around histone proteins to form nucleosomes.

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