Mutational events, which result in the deletion or addition of nucleotide bases in DNA, thereby causing gross changes in the amino acid sequences of proteins are termed as

Options

A. frame shift mutations
B. point mutations
C. forward or backward mutations
D. transversions

Answer

To solve the question regarding mutational events that result in the deletion or addition of nucleotide bases in DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about mutations that involve the deletion or addition of nucleotide bases in DNA, which lead to significant changes in the amino acid sequences of proteins.

2. **Types of Mutations**: There are several types of mutations, including:
- **Point mutations**: These involve a change in a single nucleotide base.
- **Frameshift mutations**: These occur when nucleotides are added or deleted from the DNA sequence, altering the reading frame of the genetic code.
- **Forward and backward mutations**: These refer to mutations that either revert to the original sequence or change to a different sequence.
- **Transversion**: This is a specific type of point mutation where a purine is replaced by a pyrimidine or vice versa.

3. **Focus on Frameshift Mutations**: The key aspect of the question is the impact of nucleotide addition or deletion on the reading frame of the DNA. When a nucleotide is added or deleted, it shifts the entire downstream sequence of codons, leading to a completely different sequence of amino acids in the resulting protein.

4. **Example Illustration**:
- Consider a DNA sequence: ACG TAG TAC TGA.
- If we add a nucleotide (e.g., G) after ACG, the sequence becomes: ACG G TAG TAC TGA.
- The new codons would be: ACG, GTA, CTA, GAT, etc., which are different from the original codons.
- This change in codons leads to a different sequence of amino acids in the protein, demonstrating a gross change.

5. **Conclusion**: Since the addition or deletion of nucleotides causes a shift in the reading frame and results in significant changes in the amino acid sequence, these mutations are classified as **frameshift mutations**.

### Final Answer:
The correct term for mutational events that result in the deletion or addition of nucleotide bases in DNA, causing gross changes in the amino acid sequences of proteins, is **frameshift mutations**.