How did mutation studies start?
At the beginning of this century, the Dutch biologist Hugo de Vries proposed the concept of mutation from the study of the heredity of a plant. The biologist observed that from time to time new characteristics appeared in some plants and that these characteristics were not present in their ancestors. Therefore, he concluded that these changes were caused by some sudden and accidental change in a gene, and that from then on they were transmitted to their descendants. Thus, the mutation would be responsible for the emergence of several gene alleles, triggering genetic variation in organisms.
Understanding how mutation occurs
In the DNA molecule we find genes with the characteristics of the organism. All information is encoded by a sequence of nitrogenous bases in the gene itself, and it is from this sequence of bases that the construction of a specific protein takes place. If, for any reason, there is a change in the sequence of nitrogenous bases in the DNA, there will also be change in the amino acid sequence that makes up the protein, and consequently in the properties of the protein. In fact, the change that occurred in the DNA base sequence was a
mutation, and it may be enough to provoke the appearance of a new feature in the organism.Thus, we can conclude that The mutation it is a sudden, random change in genetic material that can be passed on to offspring.
At mutations are induced by mutagenic agents, which can be of chemical or physical origin. Defect in the DNA duplication mechanism, exposure to ionizing radiation (which cause the formation of ions inside cells), such as X-rays, rays gamma and ultraviolet radiation, radioactivity, chemicals such as benzimidazole, nitrous acid, hydrazine, mustard gas and methanol increase levels in mutation of the genes of any living organism, from viruses and bacteria to plants and animals.
But maybe you're wondering, "But in living organisms are there no repair enzymes that correct DNA duplication errors and repair the damage done by mutagenic agents?".
Yes, these enzymes exist in living organisms, but repair is not always done, as the enzymes can also fail. But it's very important to remember that in the human species, where we find 3 billion base pairs nitrogenous, repair and exchange of approximately 20 base pairs per year, which represents a rate of mutation very low. This is justified by the efficient mechanism that cells have developed to correct errors that affect the DNA. In this mechanism, enzymes recognize the altered DNA and join it, cutting and eliminating the chain where the defect is. Then, other specific enzymes produce a new segment of DNA, modeled on the complementary strand, which does not contain errors, replacing the defective part. That's why the mutations genetics occur with low frequency.
At mutations can occur in any cell in the body, whether they are somatic cells (skin, liver, heart cells, etc.)or germ cells (gametes). when the mutation occurs in some somatic cell we say that there was somatic mutation. This kind of mutation it is not evolutionarily important, as it will not be passed on to descendants. If mutation occurs in some germ cell (sperm or egg) we say it happened germline mutation. In this type of mutation, the change in DNA will be passed on to offspring.
Mutations can be of two types: gene mutations and chromosomal mutations.
At gene mutation there is a change in a stretch of the DNA molecule, leading to a modification in the synthesized protein, as occurs in a disease known as sickle cell anemia.
At chromosomal mutation there is alteration of entire parts of chromosomes, changing the sequence of genes on a chromosome (structural chromosomal alterations) or even a change in the number of chromosomes (numerical chromosomal alterations).
By Paula Louredo
Graduated in Biology