In "X-Men First Class" movie, one of the characters says that a girl with heterochromia (different color eyes) is a mutant. Perhaps this is one of the most honest examples of mutations in a superhero movie. In biology, unlike in the movies, everything happens much more ordinarily, scientifically, but it is no less amazing! Indeed, the diversity of eye color, skin color, height, and even our existence as a species and everything that makes us unique, we owe to various mutations that occurred sometime long ago. But will mutations make us a superhero? Let's try to find out about it in this topic.
Classification of mutations
A mutation is a sudden, sustained, hereditary change in DNA that occurs under the influence of external or internal changes. The ability to mutate is a universal property of all life forms, from viruses and microorganisms to higher plants, animals, and humans. The process of mutation is the basis of hereditary variability in nature.
Mutations can occur in germ cells and they can be inherited during sexual reproduction. Such mutations are called Germline mutations. There are also somatic mutations.
Mutations can be divided into spontaneous and induced. Spontaneous mutations arise spontaneously, suddenly as a result of errors in the operation of DNA synthesis enzymes. Induced mutations, on the contrary, arise under the influence of mutagenic influences under artificial (experimental) conditions or adverse environmental influences. Yes, yes, you are right in thinking that the story of Deadpool, the Ninja Turtles, or Spider-Man are prime examples of induced mutations.
There are many different classifications of mutations, let us focus on the most popular amongst them – Large Scale Mutations and Small Scale Mutations.
Large scale mutations
Large Scale Mutations are fairly large mutations that change the number or structure of a cell's chromosomes. These include:
- Polyploidy – multiple increases in the number of sets of chromosomes, that is, the organism gets not 2n (a diploid set of chromosomes), but 3n, 4n, etc.
- Aneuploidy – disappearance or appearance of one chromosome in a pair (e.g. trisomy 21 chromosome).
There is a group of mutations aimed at changing the structure of the chromosome, otherwise known as chromosomal rearrangements. These include:
- Deletion – the "loss" (disappearance) of a section of a chromosome. Deletion does not necessarily occur at the edges of a chromosome, it can also occur in the center of one of its arms.
- Duplication – the doubling of a section of a chromosome.
- Inversion – a type of mutation that "turns" a section of the chromosome by 180°.
- Translocation – an exchange of sections of at least two non-homologous chromosomes.
Deletions and duplications can result in repetitive regions of the genome ranging in size from a thousand to several million base pairs. Such individual changes in the genome are called copy number variation. CNV is an important source of genetic variability.
Speaking of the effects of deletion, it is worth mentioning the emergence of fusion genes. This is the name of a gene that consists of parts of two or more different genes that form a single reading frame and is expressed as a single whole to form a compound protein (fusion protein).
Small scale mutations
Small Scale Mutations are also called point mutations – they are small mutations that can lead to great consequences or, on the contrary, change nothing. These include:
- Insertion – the appearance of one or more nucleotides in a strand of DNA. Such mutations can lead to a frameshift and disrupt proper protein synthesis.
- Deletion – on the contrary, removal of one or more nucleotides from the DNA strand. This type of mutation can also lead to a frameshift and have a significant impact on the correct functioning of a gene.
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Substitution of a single nucleotide mutation. It's time to talk about the phenomenon of single nucleotide polymorphism. SNP is a single-nucleotide difference in DNA sequences in identical chromosome segments. A nucleotide can be replaced so that it does not change the nature of the base (purine is replaced by purine, and pyrimidine by pyrimidine, that is adenine by guanine, and cytosine by thymine and vice versa), for example instead of GUG the triplet becomes GUA. Such substitutions are called transitions. However, if we replace the triplet with a GUU, that is, if we replace the purine base with a pyrimidine base, this would be called a transversion. This will have its own consequences for the organism, even though in all 3 cases we will get the same amino acid, valine. SNP can also occur in non-coding regions of DNA.
Conclusion
Real life is not a movie or a superhero comic book, there are no miracles, and a bite from a radioactive spider will obviously not do any good. Although some mutations are harmless, hidden, and may prove useful over time. The adaptability of evolutionary changes is a consequence of natural selection preserving the carriers of those mutations and their combinations that turn out to be useful in a given environment. Humans have learned how to induce mutations, but have not learned how to control them, so for now it is better to stay away from the harmful effects of mutagens. Mutations arise spontaneously, and uncontrollably in different parts of the cell at different levels of the organization. But even so, we have learned how to benefit from mutations by speeding up the selection process, for example.