A mutation is a change in DNA that may or may not be beneficial to the organism or cause no harm or benefit.
Mutations can be beneficial, neutral or harmful and therefore are not targeted, occurring at random. This means that a change in DNA can provide an improvement in the organism, without causing any advantage or harm or even triggering problems, as in the case of genetic diseases. Therefore, a mutation does not arise to guarantee the evolution of an organism, being completely by chance.
We can classify mutations into somatic and germline. Somatics are those that occur in cells responsible for the formation of tissues and organs (somatic cells) and, therefore, are not normally transmitted. Germline mutations, in turn, occur in cells that give rise to gametes, being, therefore, mutations that can be transmitted to the next generation.
Mutations can be either genetic or chromosomal . Gene mutations are those in which changes occur in genes , and chromosomal mutations are those in which changes occur in entire parts of chromosomes.
→ Types of gene mutation
Gene mutations can be classified as point, insertion and deletion.
- Point mutation : These mutations occur when only one base is changed. Point mutations can be classified as silent, missense and nonsense . The silent ones are those in which a base is changed, but do not affect the amino acid to be produced, that is, the code is changed, however, the encoded protein is the same. In missense mutations , the amino acid of the protein is changed, producing a different one. The nonsense mutation , in turn, is one in which a stop codon is produced, preventing the protein from being fully produced.
Insertion and Deletion Mutation: In insertion mutations, one or more nucleotides are added to the DNA. In deletion mutations, one or more nucleotides are removed, which causes changes in the protein composition.
→ Types of chromosomal mutations
Chromosomal mutations or chromosomal alterations can be numerical or structural.
- Numerical mutations: These changes are nothing more than variations in the number of chromosomes. Numerical mutations can affect the number of genomes (euploidies) or cause chromosomes to appear or appear in one of the pairs (aneuploidies). Euploidies are uncommon in humans and usually cause the death of the embryo. Aneuploidies, in turn, occur more frequently, as is the case with Down Syndrome , in which the individual has three chromosomes 21.
- Structural mutations: These mutations cause variations in the structure of chromosomes, affecting the arrangement or number of genes. In this case, they can be classified into deletion, duplication, inversion and translocation. In the deletion, there is a loss of a portion of the chromosome, which causes a decrease in genes. In duplication, chromosome enlargement and gene repetition are observed. In inversion, the break and inversion of a segment of the chromosome occurs. During translocation, the exchange of non-homologous chromosome segments occurs. As an example of structural mutations, we can mention Cri du Chat syndrome , known as Cat Meow, a problem caused by a deletion that causes facial anomalies and mental retardation.