Understanding Genetic Mutations: Types, Causes, and Evolution
Understanding Genetic Mutations
Mutations: Random alterations of genetic material, usually involving deficiencies, can be lethal. They are usually recessive and remain hidden, contributing to population variability.
Somatic Mutations
Unless they become cancer cells, somatic mutations are often irrelevant because non-viable cells can be replaced. When cells divide by mitosis, they give rise to a colony or clone of mutant cells resembling the former.
Germline Mutations
Germline mutations are transcendental, as all cells of the new body will have them. Mutations can be natural or induced by mutagens (radiation and certain chemicals).
Gene Mutations
Systems repair gene mutations.
Chromosomal Mutations
Chromosomal mutations cause changes in the internal structure of the chromosome:
- Deletion: Loss of a fragment of the chromosome. If the fragment has many genes, the deletion can have pathological consequences and even death if it affects the two homologous chromosomes.
- Duplication: Duplication of a segment of a chromosome. This increases genetic material and, through subsequent mutations, may determine the emergence of new genes during the evolutionary process.
- Inversion: Reversal of a fragment in the chromosome. If the inverted segment includes the centromere, it is called pericentric inversion; if not, paracentric inversion. Inversions do not typically prejudice the individual, but can affect descendants during meiosis if a crossover occurs within the inversion.
- Translocation: The changing position of a segment of a chromosome. Translocations usually do not harm the individual who has suffered them, but can affect their offspring, as they may inherit one incomplete chromosome or duplications. When produced by exchange of segments between two chromosomes, it is called reciprocal translocation. When there is only translation of one segment to another place on the same chromosome or other chromosomes, without reciprocity, it is called transposition.
Genomic Mutations
Genomic mutations are alterations in the number of chromosomes of a species. There are two types:
- Aneuploidy: A change in the normal number of copies of one or more chromosomes, without affecting the whole genome. An example of aneuploidy is Down syndrome (trisomy 21).
- Euploidy: Alteration in the normal number of haploids of an individual.
Causes of Genomic Mutations
- Centric fusion: Merging of two non-homologous chromosomes with loss of a centromere.
- Centric fission: Splitting of a chromosome in two.
- Segregation during meiosis wrong: Erroneous distribution of homologous chromatids between the daughter cells.
Mutagens
Factors affecting the normal frequency of mutations include:
Mutagenic Radiation
- Non-ionizing radiation: Ultraviolet rays. Electromagnetic radiation like light, but shorter wavelength.
- Ionizing radiation: Electromagnetic radiation of wavelength less than UV, such as X and gamma rays, and particulate emissions as alpha or beta radiation.
Mutagenic Chemicals
- Amendments bases: Substitution of one base for another.
- Intercalation of molecules.
Mutation and Evolution
The variability of the offspring of asexually reproducing organisms is due exclusively to mutations, and in organisms with sexual reproduction, mutations and, especially, genetic recombination that occurs in meiosis. Mutation is, from the qualitative point of view, much more important than recombination, because mutation may lead to further genes, while recombination simply creates different groups of genes. Mutation is therefore the basis of variability, and without it, there would be no evolution.