Six kingdom classification was suggested by Gray and Doolittle (1982) and Carl Woose (1990) divided these six kingdoms into three domains on the basis of sequence of

Options

A. r-RNA genes
B. m-RNA genes
C. nitrogen bases in DNA
D. amino acids in protein

Explanation

To solve the question regarding the classification of organisms into six kingdoms and their subsequent division into three domains, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Six Kingdom Classification**:
- The six kingdoms of life were proposed by Gray and Doolittle in 1982. The kingdoms are:
- **Plantae** (plants)
- **Animalia** (animals)
- **Protista** (unicellular organisms)
- **Fungi** (fungi)
- **Archaebacteria** (ancient bacteria)
- **Eubacteria** (true bacteria)

2. **Introduction of Domains**:
- In 1990, Carl Woese introduced a new classification system that divided the six kingdoms into three higher categories known as domains. This was a significant shift in biological classification.

3. **Identifying the Three Domains**:
- The three domains proposed by Carl Woese are:
- **Archaea** (which includes Archaebacteria)
- **Bacteria** (which includes Eubacteria)
- **Eukarya** (which includes Plantae, Animalia, Fungi, and Protista)

4. **Basis for Classification**:
- Carl Woese's classification into domains was based on the sequence of **16S rRNA genes**. This molecular data provided insights into the evolutionary relationships among different organisms.

5. **Choosing the Correct Option**:
- Given the options in the question, the correct answer is **option 1: rRNA genes**. This is because the classification into domains was specifically based on the sequence of these genes.

### Final Answer:
The correct answer is **option 1: rRNA genes**.

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