A component or a molecule which when incorporated into the DNA changes its genetic composition is called a mutagen.
A mutagen is a compound that might be chemical or physical in nature and cause changes in the genetic material which are heritable and irreversible. When the repair mechanism is unable to recognize the mutagenic effects, it tends to escape the lesions created by the mutagen. Such mutations or lesions become fixed with time and can be inherited by the progeny cells. The changes occurred due to mutagen are called mutations.
The mutations caused due to mutagens are known as induced mutations whereas, some mutations occur spontaneously due to DNA replication error, error in recombination and repair and are called spontaneous mutations.
The mutagens are categorized as follows:
1. Chemical mutagens
The chemical compounds such as aromatic amines, alkylating agents, and deaminating agents directly interact with the DNA and produce mutagenic effects. For example, nitrous oxide is a deaminating agent and causes cytosine to convert into uracil changing the DNA sequence. The alkylating agents result in breakages and crosslinking in the DNA by adding ethyl or methyl group to the bases.
2. Physical mutagens
The ionizing radiations, radioactive decay, and the ultraviolet radiations are the physical agents that cause mutations in the DNA. The radiations like gamma rays and X-rays result in DNA breakages. The ultraviolet radiations absorbed by the bases results in the formation of pyrimidine dimers.
3. Biological mutagens
Bacteria, viruses, and transposons act as biological agents to bring about mutation. The transposons translocate into DNA fragment and disrupt the genetic composition of the functional genes. The virus also disrupts the genetic function once incorporated into the genome. Certain bacteria produce oxidative species which cause DNA damage and increase the mutation efficiency.
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