9BBCBB4E-1964-4F5A-8FFE-F725B2C2A0DB.jpeg

# 12. Mutations and m... # **COLEGIUL NATIONAL „MIHAI VITEAZUL” PLOIESTI** PROFESSOR: Ana Marin **MUTATIONS AND MUTAGENESIS** * Mutations are permanent and irreversible modifications of genetic material structures and functions that lead to a new phenotype (or new characteristics). * The pro...

# 12. Mutations and m... # **COLEGIUL NATIONAL „MIHAI VITEAZUL” PLOIESTI** PROFESSOR: Ana Marin **MUTATIONS AND MUTAGENESIS** * Mutations are permanent and irreversible modifications of genetic material structures and functions that lead to a new phenotype (or new characteristics). * The process of the appearance of mutations is called mutagenesis and is determined by mutagenic factors. **1. Physical mutagenic factors** * Represented by: * thermal shocks (cold or hot) * non-ionizing radiation (ultraviolet radiation and electromagnetic radiation) * ionizing radiation (electromagnetic and corpuscular radiation), acceleration force etc. **2. Chemical mutagenic factors** * Represent a very wide range of chemical substances, very different in structure and action. * Among them are: caffeine, nitrogenous bases analogs, nitrous acid, some dyes, some antibiotics etc. **3. Biological mutagenic factors** * Viruses that induce modifications of genetic material, especially at the embryonic level determining teratogenic effects - serious malformations at the embryonic level. * The effects of these factors manifest themselves through: deterioration of nucleic acid structures, errors in copying information, inhibition of cell division, etc. The classification of mutations can be done according to several criteria 1. According to the mode of appearance, mutations can be: * natural - spontaneous, without human intervention * artificial - appearing through the use of mutagen factors by man in the experimental field 2. According to the type of affected cell: * somatic mutations (affect somatic cells) * gametic mutations (affecting gametes) 3. According to the type of affected chromosome: * autosomal or heterozygous chromosome mutations 4. According to the effect on health: harmless, harmful, neutral or lethal 5. According to the mode of manifestation: dominant, recessive, semidominant 6. According to the amount of affected genetic material, mutations can be: * gene mutations affecting the structure of genes, like inversions, deletions, additions or substitutions (replacing) of a nucleotide in the DNA molecule * chromosome mutations that modify the form, structure and function of chromosomes. * Genome mutations affect the number of chromosomes. * Aneuploidy consists of the presence in somatic cells of 1, or 2 chromosomes more or less, $(2n\pm1,2)$. This results from the phenomenon of nondisjunction of chromosomes (non-separation of chromosomes of a pair in time of cell division) or the appearance of some causes (fissions-chromosomal fusions). As a result of non-disjunction, gametes are formed with one chromosome more or less, which participate in fertilization, thus the organism results with: * trisomy - with one chromosome more $(2n+1)$ * tetrasomy - with two chromosomes more $(2n+2)$ * nullisomy - with two chromosomes less $(2n-2)$ * monosomy - with one chromosome less $(2n-1)$ * Polyploidy consists of the multiplication of the entire set of chromosomes of $2x, 3x, 4x, \dots nx$. Polyploid forms present characteristics such as the phenomenon of gigantism and greater resistance to stress factors. In humans, polyploidy is not compatible with survival, but it can be found in plants in cold areas where, by multiplying the number of chromosomes, the resistance to cold increases.