What are the classifications of mutations?

Mutations may be classified in a variety of ways depending on different parameters. 

Based on where they form, mutations may be classified as: 

• Germline mutations occur in a parent’s reproductive cells – sperm or egg. These mutations are especially significant as they are hereditary and can affect their offspring’s genetic makeup. Every cell in their offspring will carry this mutation.
• Somatic mutations occur in all cells in the body other than the sperm and egg.  These mutations cannot be passed on from parents to their children.  

Based on the way the genetic material gets changed, mutations may be classified as: 

• Chromosomal alterations occur when a chromosome fragment that breaks off does not rejoin properly or does not rejoin at all. These types of mutations are very serious. They change the structure of the chromosome and can result in the death of the organism. Even if the organism survives, it will be affected in some way or another. Down Syndrome is a common example of chromosomal alteration in humans. 
• Point mutations occur as a result of a change in a single nucleotide of the DNA. The way the point mutation changes the genetic code will determine the effect it has on the organism but it is usually less serious than a chromosomal alteration. Point mutations can be silent (they do not affect the protein’s functions), nonsense (they result in shortened or non-functional proteins) or missense (they cause an alteration or loss of function in protein). 
• Frameshift mutations occur when one or more nucleotides are either deleted or inserted, causing a change in the reading frame of the base sequence. When extra base pairs are inserted or added into a new place in the DNA sequence, it results in an insertion mutation. When a section of DNA is lost or deleted, it results in a deletion mutation. Base pair alteration causes an abnormal reading frame which ultimately results in an abnormal protein formation.
• Duplication mutations occur when a chromosome fails to separate from its homologous during meiosis. In this case, one gamete receives an extra chromosome copy, while the other gamete lacks it. 
• Inversion mutations reverse the direction of a chromosome fragment. In this type of mutation, some gene sequences are inverted and then inserted back into the original sequence. 
• Translocation mutations: In this type of mutation, a chromosome fragment breaks off and attaches to another chromosome.