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Chapter 15: Problem 8

What is the difference between a silent mutation and a neutral mutation?

Short Answer

Expert verified
Answer: The key differences between silent and neutral mutations include: 1. Silent mutations only involve changes in the DNA sequence that do not alter the amino acid sequence, while neutral mutations can involve changes in both coding and non-coding regions of the DNA. 2. Silent mutations result from the redundancy in the genetic code, where different codons code for the same amino acid, while neutral mutations can cause a change in the amino acid sequence, but the substitutions do not impact protein function. 3. While silent mutations are generally always neutral in effect, not all neutral mutations are silent, as some have altered amino acid sequences without impacting the organism's fitness or protein function. In terms of protein synthesis and gene expression, silent mutations do not affect the amino acid sequence of the protein being produced, and therefore do not change the function of the protein. On the other hand, neutral mutations can be present in coding or non-coding regions and may result in changes to the amino acid sequence. However, these changes do not have a significant impact on the protein's functionality or the organism's fitness.

Step by step solution

01

Define a Silent Mutation

A silent mutation is a change in a DNA sequence that does not affect the amino acid sequence of the protein being produced. This occurs because different codons (a triplet of nucleotides) can code for the same amino acid, a concept known as redundancy or degeneracy of the genetic code. Silent mutations result from a change in the DNA sequence that still leads to the same amino acid being incorporated into the protein, and therefore does not change the function of the protein.
02

Define a Neutral Mutation

A neutral mutation is a change in the DNA sequence that does not significantly affect the function or fitness of the organism. Neutral mutations can be present in coding regions and non-coding regions. In the coding regions, neutral mutations can result in a change in the amino acid sequence, but the substitution does not impact the protein's functionality. In non-coding regions, the mutation does not affect regulatory elements or gene expression, which may have an impact on the organism's fitness.
03

Key Differences between Silent and Neutral Mutations

While both silent and neutral mutations do not have significant functional consequences for the organism, there are some key distinctions between them: 1. Silent mutations only involve changes in the DNA sequence that do not alter the amino acid sequence, while neutral mutations can involve changes in both coding and non-coding regions of the DNA. 2. Silent mutations result from the redundancy in the genetic code, where different codons code for the same amino acid. In contrast, neutral mutations can cause a change in the amino acid sequence, but the substitutions do not impact protein function. 3. While silent mutations are generally always neutral in effect, not all neutral mutations are silent, as some have altered amino acid sequences without impacting the organism's fitness or protein function. In summary, the main difference between a silent mutation and a neutral mutation is that silent mutations deal exclusively with no change in the amino acid sequence, while neutral mutations encompass a broader range of mutations that may or may not affect amino acid sequences, as long as they do not have a significant impact on the organism's function or fitness.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Silent Mutation
Understanding silent mutations is essential when studying genetic variations. These mutations occur within the DNA sequence but, intriguingly, do not alter the protein's amino acid sequence. This can happen due to the way genetic code operates. There are multiple codons, each made up of three nucleotides, that can code for the same amino acid. For example, the amino acid Leucine can be coded by six different codons. So, a change in the third nucleotide often doesn't affect the amino acid sequence, thanks to this built-in genetic code redundancy.

What makes silent mutations fascinating is their 'covert' nature. They can slide through the DNA without causing a ripple in the phenotype—that is, there's no observable change in the organism's traits. This can be useful during genetic screening or studies related to evolutionary genetics, where mutations without phenotypic effects have significant interest.
Neutral Mutation
Moving on to neutral mutations, these are changes to the DNA sequence that, unlike some other mutations, do not impact an organism's ability to survive and reproduce. In other words, they are mostly 'invisible' to natural selection. These mutations may not even result in a different amino acid sequence (though they can), and even if they do, the new amino acid doesn't alter the protein's function.

Neutral mutations can take place within both coding and non-coding regions of DNA. Even in coding regions, the change in the amino acid might be in a part of the protein not critical to its function, or the substitution could involve amino acids with similar properties—meaning the overall structure and function of the protein remain unchanged. Such mutations provide a wealth of information for evolutionary biologists, as their accumulation over time can be used to study the history and relationships between different species.
Genetic Code Redundancy
The genetic code redundancy is an interesting and vital concept to grasp when delving into genetics. It refers to the fact that the genetic code is degenerate—meaning that most amino acids are encoded by more than one codon. This redundancy acts as a buffer against mutations; it allows a certain degree of flexibility and 'forgiveness’ in the genetic coding, which can be pivotal for an organism’s survival.

For example, with four bases and three positions in a codon, there are 64 possible combinations, but there are only 20 standard amino acids. As a result, many amino acids are encoded by multiple codons. This redundancy is not evenly distributed; for some amino acids, there's a wide range of codons, while, for others, the options are more limited. Understanding this concept is crucial as it explains why some DNA sequence changes do not alter the resulting protein and have no significant biological effect.
DNA Sequence Changes
DNA sequence changes are at the heart of genetic mutations. These alterations can be as minimal as a single nucleotide variation—known as a point mutation—or they can span large sections of DNA through deletions, insertions, or rearrangements.

The impact of these changes on an organism can be vast and varied. Some lead to diseases, while others might provide evolutionary advantages. In the classroom or laboratory, distinguishing between different types of mutations helps students and researchers understand how genetic variation contributes to biodiversity and evolutionary processes. In essence, it's the study of these changes that propels us to a deeper comprehension of life's diversity and the mechanics of heredity. DNA sequence changes are the ultimate source of genetic diversity, and understanding them is key to grasping the full picture of genetics.

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Most popular questions from this chapter

Most mutations in a diploid organism are recessive. Why?

Most mutations are thought to be deleterious. Why, then, is it reasonable to state that mutations are essential to the evolutionary process?

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?

Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?

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.
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