[A] : Organisms that bear large number of common amino acid sequence may be considered to be more closely related than to those with greatly different amino acid sequence.
[R]: The proteins are chemical finger prints of evolutionary history because they bear amino acid sequences that have changed as a result of genetic change

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the question regarding the relationship between organisms based on amino acid sequences and the explanation of proteins as chemical fingerprints of evolutionary history, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Amino Acid Sequences**:
- Amino acids are the building blocks of proteins. The sequence of amino acids in a protein is crucial for its function and is determined by the genetic code.

2. **Comparing Amino Acid Sequences**:
- When comparing two organisms, if they share a large number of common amino acid sequences, it indicates that they may have a closer evolutionary relationship. This is because similar sequences suggest that the organisms have diverged from a common ancestor more recently than those with significantly different sequences.

3. **Significance of Sequence Similarity**:
- The degree of similarity in amino acid sequences can be quantitatively assessed. A high percentage of similarity (e.g., 33.33% or more) can be used to classify organisms as homologous, indicating they share a common ancestor.

4. **Role of Mutations**:
- Mutations in the amino acid sequences occur over time due to evolutionary pressures. These changes can lead to adaptations in organisms, but they also provide a record of evolutionary history. The more mutations that have occurred, the more distantly related the organisms may be.

5. **Proteins as Evolutionary Indicators**:
- Proteins serve as chemical fingerprints of evolutionary history because their sequences reflect the genetic changes that have occurred over time. Conserved sequences are indicative of essential functions that have remained unchanged, while variable sequences may reflect adaptations to different environments.

6. **Conclusion**:
- Both the assertion (A) and the reason (R) are true. Organisms with a high degree of similarity in amino acid sequences are more closely related, and proteins indeed act as chemical fingerprints that reveal the evolutionary history of organisms.