Question

What is a spontaneous mutation, and why are spontaneous mutations rare?

Short answer

A spontaneous mutation is a natural change in an organism's DNA that occurs without any external factors, such as radiation or chemical exposure, influencing it. These mutations can result from replication errors during DNA synthesis, random movement of DNA molecules, or other molecular processes. The rarity of spontaneous mutations can be attributed to several factors, including the use of high-fidelity DNA polymerases for replication, the presence of various DNA repair mechanisms, and the redundancy in the genetic code that allows some mutations to be silent and not affect the organism.

Step-by-step solution

Define a spontaneous mutation

A spontaneous mutation is a change in an organism's DNA that occurs naturally and without any external factors, such as radiation or chemical exposure, instigating it. These mutations can arise due to replication errors during DNA synthesis, random movement of DNA molecules, or other molecular processes.

Discuss the frequency of spontaneous mutations

The frequency of spontaneous mutations is relatively low. This is due to the presence of various cellular processes that act as safeguards to maintain the integrity of an organism's genetic code. These include: 1. High-fidelity DNA polymerases: These enzymes are responsible for replicating DNA during cell division and possess proofreading capabilities. They can recognize and correct errors made during DNA synthesis. 2. DNA repair mechanisms: There are several DNA repair pathways in cells, such as base excision repair, mismatch repair, and nucleotide excision repair, that work to recognize and fix any errors or damage that may have occurred during DNA replication. 3. Redundancy in the genetic code: The genetic code is degenerate, meaning that multiple sequences of three nucleotides (codons) can specify the same amino acid. This redundancy allows some mutations to be silent, meaning they don't lead to a change in the amino acid sequence of the protein, and therefore, have no effect on the organism. These factors all contribute to the rarity of spontaneous mutations, as they work to minimize the occurrence and impact of such events on an organism's genetic information.