Thte ultimate biological unit which controls heredity, is called :

Options

A. Genome
B. Chromosome
C. Genotype
D. Gene

Answer

To solve the question "The ultimate biological unit which controls heredity, is called:", we need to analyze the options provided and determine which one accurately represents the unit of heredity.

### Step-by-Step Solution:

1. **Understanding the Question**: The question is asking for the fundamental biological unit that is responsible for heredity.

2. **Analyzing the Options**:
- **Option 1: Genome**:
- The genome is the complete set of genetic information in an organism. It includes all the DNA and genes but is not the smallest unit that controls heredity.
- **Conclusion**: Incorrect option.

- **Option 2: Chromosomes**:
- Chromosomes are structures within the cell nucleus that contain DNA. They are made up of DNA and proteins but represent a larger structure that contains many genes.
- **Conclusion**: Incorrect option.

- **Option 3: Genotype**:
- The genotype refers to the genetic makeup of an organism, which includes all the genes it possesses. However, it is not the smallest unit of heredity.
- **Conclusion**: Incorrect option.

- **Option 4: Gene**:
- A gene is defined as the basic unit of heredity. It is a segment of DNA that contains the information necessary to produce a specific trait. Genes can exist in different forms called alleles, which are responsible for variations in traits.
- **Conclusion**: Correct option.

3. **Final Answer**: The ultimate biological unit which controls heredity is called a **gene**.