Biological unit controlling heredity is

Options

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

Answer

**Step-by-Step Solution:**

1. **Identify the Biological Unit of Heredity:**
The question asks for the biological unit that controls heredity. The fundamental unit of heredity is known as a gene.

2. **Define a Gene:**
A gene is described as the basic physical and functional unit of heredity. It carries the instructions for making proteins, which are essential for the structure and function of living organisms.

3. **Composition of Genes:**
Genes are composed of DNA (deoxyribonucleic acid). DNA contains the genetic instructions used in the development and functioning of all known living organisms.

4. **Function of Genes:**
While most genes code for proteins, some genes do not code for proteins but still play crucial roles in regulating various biological processes.

5. **Clarification of Related Terms:**
- **Genome:** Refers to the complete set of genetic information in an organism, which is found within the chromosomes.
- **Chromosome:** A thread-like structure made up of proteins and a single DNA molecule that carries genetic information.
- **Genotype:** The complete set of genes present in an individual, which determines specific traits.

6. **Conclusion:**
Based on the definitions and explanations provided, the biological unit controlling heredity is the gene.

**Final Answer:** The biological unit controlling heredity is the **gene**.

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