Types of DNA Mutations and Examples

In this types of DNA mutations and examples post we have briefly explained about causes of DNA mutations in humans and consequences of DNA mutations in humans.

DNA mutations in humans is a permanent change in the sequence of DNA. In order for an observable effect, mutations must occur in gene exons or regulatory elements. Changes in the non-coding regions of DNA (introns and junk DNA) generally do not affect function.

Causes

DNA mutations in humans can be caused by external (exogenous) or endogenous (native) factors or they may be caused by errors in the cellular machinery. Physical or chemical agents that induce DNA mutations in humans are called mutagens and are said to be mutagenic.

Exogenous factors: environmental factors such as sunlight, radiation, and smoking can cause mutations. Endogenous factors: errors during DNA replication can lead to genetic changes as can toxic by-products of cellular metabolism.

Consequences

DNA mutations in humans can be advantageous and lead to an evolutionary advantage of a certain genotype. DNA mutations in humans can also be deleterious, causing disease, developmental delays, structural abnormalities, or other effects.

DNA Mutations in Humans

Deletion

Genetic material is removed or deleted. A few bases can be deleted or it can be complete or partial loss of a chromosome.

DNA Mutation

Frameshift

The insertion or deletion of a number of bases that is not a multiple of 3. This alters the reading frame of the gene and frequently results in a premature stop codon and protein truncation.

DNA Mutation

Insertion

When genetic material is put into another region of DNA. This may be the insertion of 1 or more bases, or it can be part of one chromosome being inserted into another, non-homologous chromosome.

DNA Mutation

Missense

A change in DNA sequence that changes the codon to a different amino acid. Not all missense DNA mutations in humans are deleterious, some changes can have no effect. Because of the ambiguity of missense DNA mutations in humans, it is often difficult to interpret the consequences of these mutations in causing disease.

Nonsense

A change in the genetic code that results in the coding for a stop codon rather than an amino acid. The shortened protein is generally non-function or its function is impeded.

Point

A single base change in DNA sequence. A point DNA mutations in humans may be silent, missense, or nonsense.

Silent

A change in the genetic sequence that does not change the protein sequence. This can occur because of redundancy in the genetic code where an amino acid may be encoded for by multiple codons.

Splice Site

A change in the genetic sequence that occurs at the boundary of the exons and introns. The consensus sequences at these boundaries signal where to cut out introns and rejoin exons in the mRNA. A change in these sequences can eliminate splicing at that site which would change the reading frame and protein sequence.

Translocation

A structural abnormality of chromosomes where genetic material is exchanged between two or more non-homologous chromosomes.

Further Readings

Reference