When an alteration occurs in a sequence of DNA, leading to a change in the message being carried by the gene, a mutation is said to have occurred. Some mutations are harmful, some beneficial, while others are silent. Mutations leading to resistance to HIV are beneficial. When there is a change in a DNA sequence that does not affect the sequence of the amino acid that is produced, it is known as silent mutation. For instance, a change from AAA to AAG will still lead to the production of lysine.
Classification of mutations
There are different types of mutations. They include deletions, insertions, inversions, and substitutions among others. These can be classified into point mutation, copy number variation, and chromosomal mutation. In point mutation, there is an alteration in a single DNA base. This alteration can be a substitution, where there is a nucleotide replacement with another. It is this type of mutation that occurs in sickle cell anemia. When a nucleotide is omitted during replication, it is known as deletion and can be seen in cystic fibrosis. The addition of one or more base pairs during DNA replication is called insertion, and it is noted in some beta-thalassemias.
Deletions and duplications of genetic sequences that are large, greater than 1kb are called copy number variations. They can lead to gene expansions or an increase in the number of triplets in the mutated genes when compared to normal genes. These can result in disorders like Friedreich’s ataxia, Fragile X syndrome, and Huntington’s disease.
Chromosomal mutations Involve structural or numerical changes to chromosomes. They may also result from deletions, insertions, translocations, duplications, and inversions. In translocations, there is a transfer of chromosome segments. Duplications occur when DNA segments are replicated. In inversions, there is an end-to-end reversal of chromosome segments. These mutations lead to Chromosomal disorders like Klinefelter syndrome, Down syndrome, Turner syndrome, and Edward syndrome.
Mutations can also occur in germ cells. Such mutations can be transferred to the offspring of the carrier. Somatic mutations are mutations that occur in cells of the body excluding germ cells. They are not transferred to one’s offspring. Exposure to radiation, and some chemicals, can also result in mutations.
Among the mutations, inversions are not easy to analyze. Hence, they were not fully understood. This challenge to understand inversions better was taken up by some scientists at EMBL Heidelberg. They studied about 40 recurrent genomic inversions. The location and the processes involved in the formation of inversion were discovered. It was also discovered that inversions were some of the fastest and most common mutations that occur in humans.
The DNA sequence in the regions where inversions occur usually flips back and forth. In these unstable regions, some critical human genes were found. Diseases like hemophilia A, neuropsychiatric disorders, and leukemias have been associated with inversions. In children, it can also cause a delay in development.
In diseases like autism in children, rare rearrangements of the genome due to inversions were noted. The researchers believe that some arrangements at the side of the inversions are either protective or predispose an individual and their offspring to these diseases. This can help in the identification of families that are susceptible to these diseases.
Mutations of genes and chromosomes are important causes of disorders like Down syndrome, sickle cell anemia, and fragile X syndrome. They can take the form of inversion, duplication, deletion, and translocation.
In this research, the inversion that was initially difficult to analyze was studied. And it was found to be a very common mutation. This study also provides a tool that will help in understanding the origin of some diseases, and identification of susceptible families.
Mutations have been noted to cause many disorders, both the ones that are transmissible to one’s offspring and the ones that are not. The study of inversion, one type of mutation, will help in understanding some diseases. Further studies might help in better management of such diseases.