Which of the following mutations would be most likely to have a harmful effect on an organism? a. a deletion of three nucleotides near the middle of a gene b. a single nucleotide deletion in the middle of an intron c. a single nucleotide deletion near the end of the coding sequence d. a single nucleotide insertion downstream of, and close to, the start of the coding sequence

Verified step by step guidance

1. Identify the type of mutations listed and understand their general impact on gene function. Deletions and insertions can disrupt the reading frame (frameshift mutations), while mutations in introns might not affect the protein if they do not alter splicing.
2. Analyze option a: A deletion of three nucleotides near the middle of a gene. This could remove an amino acid but may not cause a frameshift mutation, potentially having a less severe effect if the deleted amino acids are not critical for protein function.
3. Analyze option b: A single nucleotide deletion in the middle of an intron. Introns are non-coding regions and are spliced out during mRNA processing. This mutation is less likely to affect the protein unless it alters the splicing machinery.
4. Analyze option c: A single nucleotide deletion near the end of the coding sequence. This could cause a frameshift mutation altering the final part of the protein, potentially disrupting its function or stability.
5. Analyze option d: A single nucleotide insertion downstream of, and close to, the start of the coding sequence. This mutation is likely to cause a frameshift right from the start of the protein, altering the entire amino acid sequence and likely rendering the protein nonfunctional.

Key Concepts

Mutation Types

Mutations are changes in the DNA sequence that can affect gene function. They can be classified into several types, including deletions, insertions, and substitutions. Deletions remove nucleotides from the sequence, while insertions add nucleotides. The location and type of mutation can significantly influence whether it is harmful, neutral, or beneficial to the organism.

Frameshift Mutations

Frameshift mutations occur when nucleotides are inserted or deleted from the DNA sequence in numbers that are not multiples of three. This shifts the reading frame of the genetic code, potentially altering every amino acid downstream of the mutation. Such mutations often lead to the production of nonfunctional proteins, making them more likely to have harmful effects compared to other types of mutations.

Coding vs. Non-Coding Regions

Genes consist of coding regions (exons) that dictate protein sequences and non-coding regions (introns) that do not code for proteins. Mutations in coding regions are generally more impactful on protein function than those in non-coding regions. Understanding the distinction between these regions is crucial for predicting the potential effects of mutations on an organism's phenotype.