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Chapter 14: Problem 3

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

Short Answer

Expert verified
Answer: A spontaneous mutation is a random change in the genetic sequence that occurs during the normal processes of DNA replication or repair without any external factors. Spontaneous mutations are rare events because the DNA replication and repair processes have high fidelity, proofreading and repair systems effectively correct most errors, and spontaneous chemical reactions causing mutations occur infrequently in cellular conditions.

Step by step solution

01

Define spontaneous mutation

A spontaneous mutation is a random change in the genetic sequence that occurs during the normal processes of DNA replication or repair, without any external factors such as chemicals or radiation. These can include base pair substitutions, insertions or deletions, and chromosome rearrangements.
02

DNA replication and repair mechanisms

Spontaneous mutations occur due to errors in DNA replication and repair mechanisms. For example, DNA polymerase, the enzyme that synthesizes new DNA strands, may occasionally incorporate the wrong base during replication, leading to a mismatch. Another cause of spontaneous mutation may arise from damaged or altered bases, which can result from spontaneous chemical reactions, such as depurination or deamination.
03

Proofreading and repair systems

Most organisms have proofreading and repair systems that detect and correct errors during DNA replication or repair. For example, DNA polymerase has a proofreading function that helps identify and correct any misincorporated bases. Additionally, mismatch repair proteins can recognize and repair mismatched base pairs that may have escaped the proofreading process. These molecular mechanisms work together to maintain the fidelity of the genetic code.
04

Reasons for rarity

Spontaneous mutations are rare events for several reasons: 1. The high fidelity of DNA replication and repair processes minimizes errors. 2. Proofreading and repair systems effectively correct most mistakes that do occur. 3. Spontaneous chemical reactions that cause mutations are infrequent and occur at relatively low rates in cellular conditions. In summary, a spontaneous mutation is a random alteration in the genetic sequence that arises during DNA replication or repair. These mutations are rare due to the high fidelity of these processes and the efficiency of the proofreading and repair systems in correcting errors.

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Most popular questions from this chapter

In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, (a) How do we know that many cancer-causing agents (carcinogens) are also mutagenic? (b) How do we know that certain chemicals and wavelengths of radiation induce mutations in DNA? (c) How do we know that DNA repair mechanisms detect and correct the majority of spontaneous and induced mutations?

It has been noted that most transposons in humans and other organisms are lacated in noncoding regions of the genome regions such as introns, pseudogenes, and stretches of particular types of repetitive DNA. There are several ways to interpret this observation. Describe two possible interpretations. Which interpretation do you favor? Why?

Describe how the Ames test screens for potential environmental mutagens.Why is it thought that a compound that tests positively in the Ames test may also be carcinogenic?

A significant number of mutations in the \(H B B\) gene that cause human \(\beta\) -thalassemia occur within introns or in upstream noncoding sequences. Explain why mutations in these regions often lead to severe disease, although they may not directly alter the coding regions of the gene.

Why would a mutation in a somatic cell of a multicellular organism not necessarily result in a detectable phenotype?
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