Question

List two types of mutations that can alter the reading frame

Short answer

The two types of mutations that can alter the reading frame are Insertion Mutations and Deletion Mutations.

Step-by-step solution

Understanding Mutations

Let's first understand what a mutation is. In the genetics context, a mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.

Identifying mutation types

There are several types of mutations, such as substitution mutations, deletion mutations, insertion mutations, etc. From these, two types that can alter the reading frame are insertion and deletion mutations.

Explaining Insertion Mutations

Insertion mutations are mutations in which extra base pairs are inserted into a new place in the DNA. This addition causes a shift in the reading frame, altering downstream codons.

Explaining Deletion Mutations

Deletion mutations are mutations in which a section of DNA is lost, or deleted. Like insertion mutations, these types can also cause a shift in the reading frame, altering downstream codons.

Key concepts

Reading Frame

A reading frame is a way of dividing the sequence of nucleotides in DNA into a set of consecutive, non-overlapping sequences, known as codons. Each codon consists of three nucleotides, and these codons specify the amino acids that make up proteins.
The proper reading of these codons is crucial because it determines how DNA is translated into proteins.

• A sequence has three possible reading frames per strand, depending on where you start reading it.
• Only one reading frame is typically used, known as the open reading frame (ORF).
• If shifted, the reading frame can change the meaning of all downstream codons.

That's why alterations like insertion or deletion mutations can be so disruptive, they affect how the DNA is read and interpreted.

Insertion Mutations

Insertion mutations occur when additional nucleotides are inserted into a DNA sequence. This addition disrupts the normal reading frame by adding extra base pairs.
For example, if one nucleotide is added, every codon from the point of insertion changes, shifting the reading frame.

• The insertion changes DNA's sequence and often results in nonfunctional proteins because the original codon groupings are altered.
• Depending on the number of bases inserted, an insertion mutation might or might not disrupt the entire reading frame.
• They are particularly harmful if the number of added nucleotides isn't a multiple of three, as only then the reading frame is restored.

This can lead to significant biological consequences, including diseases.

Deletion Mutations

A deletion mutation involves the loss of one or more nucleotides from a DNA sequence. Similar to insertion mutations, deletions can shift the reading frame, affecting all downstream codons.
For example, removing just a single nucleotide alters every codon afterward, potentially changing the resulting protein entirely.

• Deletion mutations can either be single nucleotide deletions or larger sequence deletions.
• Like insertions, their disruptive effect is more severe when the number of bases lost isn't a multiple of three.
• The reading frame change can lead to creating dysfunctional proteins.

Such mutations are significant in genetic diseases, as they can drastically alter gene function.

DNA Sequence Alterations

DNA sequence alterations result from changes in the nucleotides within the DNA. Mutations are a primary source of such changes.
The causes of these alterations can be varied, including replication errors or external environmental factors.

• Changes in the DNA sequence can range from a single nucleotide substitution to large-scale rearrangements of chromosomes.
• While some alterations are harmless, others change the genetic makeup significantly.
• Mutations like insertions or deletions typically have more influential repercussions on the encoded proteins.

The impact of these changes ranges significantly, from benign changes to those causing severe genetic disorders.