Page 195 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

Mutation

Definition

A mutation is a change that occurs in our DNA sequence.

The cell in which a mutation has occurred is called mutant cell

Effect of mutation

Mutations can be:
1. No effect or neutral effect
• Some mutations don’t have any noticeable effect on the organism. Perhaps the

mutation occurs in a protein-coding region, but does not affect the amino

acid sequence of the protein.

• Other mutations have a noticeable effect, but one that doesn’t

seem to help or hurt.

• For example, a single mutation caused this cat’s ears to curl

backwards slightly, a trait that doesn’t seem to affect its health.

2. Detrimental effect

Detrimental mutations known as lethal disrupt DNA critical to survival and

cause the death of the organism

3. Beneficial effect

Other mutations are helpful to the organisms that carry them.

For example, antibiotic resistance in bacteria.

Classification of mutation

Gene mutations can be classified in two major ways:

I- Spontaneous mutations:

• Occurs at low frequency.

General Microbiology & Immunology (PM 401) theoretical handbook Page 184