Different Types of Mutations

Mutations are random or sudden variations or changes in the genetic sequence of a genome. Some mutations cause a lethal impact as well as are the causative agent of genetic disorders or cancer. On the contrary, some mutations change genetic and physical characteristics but otherwise remain harmless. Mutations can be a single nucleotide base change or change in the chromosomal segment. The mutations are either inherited or acquired. The inherited mutations passed from parents to offspring are called germinal mutations. The acquired mutations are due to environmental exposure and are also known as somatic mutations. The following topic describes all types of mutations that might occur in a genetic sequence. 

Various types of Mutations

• Germinal mutations are those which are inherited from the parents to the offspring. The mutation is hereditary and occurs in the egg or the sperm, leading to its transfer to the child. 
• The germinal mutations affect almost all the cells in the body. Small inherited changes can cause a lot of differences like genetic syndrome, genetically inherited disease, and even the risk of cancer. However, it is rare as in the majority of the cases, the inherited diseases are recessive. 
• The acquired or somatic mutations are not inherited, but either induced or spontaneous. The induced mutations are caused due to exposure to UV rays, X-rays, chemicals and other environmental agents. Spontaneous mutations are those which occur without any exposure to an environmental agent. 

Frameshift Mutations 

• Triplet codons are a string of three nucleotides which represent the amino acid or stop codon. The frameshift mutation occurs when a mutation disrupts the normal reading frame, leading to the entire genetic sequence being read incorrectly.
• When frameshift mutations occur in the germinal mutations, it can cause adverse impacts or genetic conditions. 
• Insertion and deletion are two types of mutations which can cause frameshift mutations. It can alter the gene and hence the message is no longer read correctly. 
• Insertions are the types of mutations which add extra base pairs or nucleotides in the genetic sequence, shifting the reading frame. For example, if there is a sequence AUG-CAG-UCG and inserting an A after AUG, it would shift the frame to AUG ACA GUC G. 
• Deletion mutations occur when a section of DNA is lost or deleted or even a single nucleotide is deleted leading to shifting of the reading frame. In the case of the AUG CAG UCG, on deleting, if G is deleted from CAG, it would shift the frame to AUG CAU CG. 

Point Mutations 

The points mutations can stem from both germinal mutations and somatic mutations. It is the change in the single nucleotide in the genetic sequence and is also referred to as point substitution mutations. 

It is further categorised into four types:

• Silent mutations are when the replacement of a nucleotide base does not change the amino acid in the genetic sequence. 
• Missense mutation leads to the formation of entirely different amino acids.
• A nonsense mutation is when the substitution of a single nucleotide leads to the formation of a stop codon. 
• The nonstop mutation is when the otherwise stop codon is changed into an amino acid codon.  

Substitution Mutations 

• The substation mutation is the exchange of one base for another. It is of two types, which are transition and transversion mutations. 
• Transition mutations are those which substitute purines for purines and pyrimidine for pyrimidine. 
• Transversion mutations substitute a purine for pyrimidine and vice versa. 

Chromosomal Mutation

These are large scale mutations which are also known as chromosomal rearrangements or chromosomal aberrations. Chromosome mutations alter the DNA sequence, and hence are responsible for causing several genetic syndromes. Structural mutations are any changes in the structure of the chromosome which affect the organisms. Here are some structural mutations which cause chromosomal changes.

• Chromosomal inversions are those in which a chromosome segment is broken and the broken segments rotate by 180° to rejoin. 
• Chromosomal translocation is the interchange of chromosome segments between non-homologous chromosomes. 
• Chromosome deletion is when a DNA segment is lost from one arm of chromosomes. Also, two segments on either side of deleted parts join together. 
• Chromosomal duplication is the duplication of the DNA segment within an arm of a chromosome, leading to the segment getting duplicated or copied. 

The change in the number of chromosomes is called numerical chromosome mutations. Most chromosome aberrations can lead to genetic disease or syndrome. There are many genetic disorders caused by germinal mutations due to changes in the chromosomal numbers.  

Conclusion 

A single type of mutation can cause a lot of changes in the genetic sequence and impact the chromosomal structure. During the process of DNA replication, transcription, and translation if the error is not corrected, it leads to mutation. The random or sudden change in the nucleotide base can affect both somatic and germ cells. Germinal mutations are majorly known for causing cancer, genetic disorders, and other lethal effects. Mutations are of different types like frameshift mutation (insertion or deletion), point mutations (majorly the substitution), or large chromosome mutations. In summary, there are some mutations that are silent and do not cause any impact, while some result in adverse genetic changes.