The least level of chromosome organization is

Options

A. solenoid
B. 30 nm fibre
C. nucleosome
D. none of these

Answer

To determine the least level of chromosome organization, we need to understand the structure of chromatin and how DNA is organized within it. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Chromatin Structure
Chromatin is a complex of DNA and proteins found in the nucleus of eukaryotic cells. It plays a crucial role in packaging DNA into a more compact, dense shape, allowing it to fit within the cell nucleus.

**Hint:** Chromatin consists of DNA and proteins, and its organization is essential for DNA packaging.

### Step 2: Identify the Basic Unit of Chromatin
The basic unit of chromatin is the nucleosome. A nucleosome consists of a segment of DNA wrapped around a core of histone proteins. Each nucleosome is approximately 10 nanometers in diameter.

**Hint:** The nucleosome is the fundamental building block of chromatin, made up of DNA and histones.

### Step 3: Recognize the Role of Histones
Histones are positively charged proteins that interact with negatively charged DNA due to the presence of phosphate groups in the DNA backbone. There are five main types of histones: H1, H2A, H2B, H3, and H4.

**Hint:** Histones help in the organization of DNA by forming nucleosomes.

### Step 4: Examine Other Levels of Organization
Beyond nucleosomes, DNA can be further organized into higher-order structures such as the 30 nanometer fiber (also known as solenoid structure), which is formed by the coiling of nucleosomes. This structure is more compact than nucleosomes alone.

**Hint:** Higher levels of organization include structures like the 30 nm fiber, but we are looking for the least level.

### Step 5: Conclusion
Since the nucleosome is the smallest structural unit of chromatin organization, it represents the least level of chromosome organization. Other options like solenoid and 30 nanometer fiber are higher levels of organization.

**Final Answer:** The least level of chromosome organization is the **nucleosome**.