Medical Genetics - V. M. Zaporozhan 2005

Etiology of Hereditary Diseases
Classification of Mutations
Spontaneous and Induced Mutations

Spontaneous Mutations occur under normal (natural) conditions without the targeted influence

of any mutagen on the Organism. This group includes mutations caused by endogenous factors (chemical modification of purine and pyrimidine bases within Cells, leading to their pairing with non-complementary nitrogenous bases, the presence of free radicals, errors in DNA Replication and Repair, etc.) and natural Environmental Mutagens (cosmic ionizing radiation, ultraviolet solar radiation).

Only 1/10 to 1/4 of spontaneous mutations can be attributed to the natural Background radiation, the action of free radicals and peroxides, and the thermal motion of atoms in nucleic acid molecules. The majority of spontaneous mutations arise due to errors in the Enzymes responsible for METABOLISM/36.html">DNA replication, repair, Gene recombination during Crossing-over, and other processes.

Induced mutations occur under The Influence of a known mutagenic factor (i.e., one that causes the mutation). Just like spontaneous mutations, Mutagenic Factors disrupt DNA replication, repair, gene recombination, and chromosome segregation, and can cause single- or double-strand DNA breaks. They may be of chemical, physical, or biological origin.

Table 2.1. Classification of Mutations

Mutation Classification

Selection/21.html">Types of mutations

Depending on the causes of the mutation

— spontaneous, arising without apparent causes;

— induced mutations, caused by the action of a known mutagenic factor

Depending on the possibility of inheritance

— somatic, occurring in somatic cells;

— germline, occurring in sex cells

According to the nature of genotype alteration

— Gene Mutations — alterations of genes;

— chromosomal mutations or Chromosomal aberrations — alterations in Chromosome Structure;

— genomic mutations — changes in chromosome number

According to phenotypic manifestation

— dominant or recessive;

— lethal, semi-lethal, neutral, beneficial


Last update: 11/08/2026

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