Mutation – Pathogenesis, Mechanism, Classification, Inheritance

Mutation – a change in heredity, leading to the emergence of a new trait; the mutation is fixed in the genotype and passed on to subsequent generations. The smallest part of a DNA molecule, a change in which leads to a mutation, is called a muton. The mutation-inducing agent is called a mutagen.


  1. Gene (point) – dominant, recessive, gametic, somatic.
  2. Chromosomal.
  3. Genomic.


  1. Morphological.
  2. Physiological.
  3. Biochemical.

A gene ( point , true) mutation is a change in the internal organization of a chromosome at the level of individual genes, indiscernible with a microscope; is detected by the appearance in the offspring of an altered trait. Gene mutations can be: 1) spontaneous (spontaneous); they occur out of direct connection with any physical or chemical factor in the external environment; 2) induced; they are deliberately caused by the action of factors of a known nature on the organism.


  1. Monogenic – strictly inherited (mutations of one gene).
  2. Polygenic – with a hereditary predisposition (mutations of many genes).


  1. Violation of the “gene – structural protein” – malformations.
  2. Violation of “gene – transport protein” – functional diseases.
  3. Violation “gene – protein – enzyme” – hereditary fermentopathies.

Chromosomal diseases are associated with structural or numerical abnormalities in autosomes or sex chromosomes. Usually not inherited.

Rearrangements in chromosomes are divided into the following

  1. Intrachromosomal:
    1. deletion – loss of a part of the chromosome;
    2. duplication – doubling or multiplication of some parts of chromosomes;
    3. inversion – rotation of a chromosome fragment by 180 0 with a change in the sequence of the location of genes.
  2. Interchromosomal.
    1. Translocation is the exchange of sections of non-homologous chromosomes.
  3. Combined.

By genomic mutations include the following

1. Aneuploidy, i.e. change in the number of individual chromo

catfish – the absence (monosomy) or the presence of additional (trisomy, tetrasomy, in the general case polysomy) chromosomes or the so-called unbalanced chromosome set.

2. Haploidy.

3. Polyploidy.

Haploidy and polyploidy is a decrease or increase in the number of chromosome sets of somatic cells compared to diploid.


  1. Autosomal dominant – homozygote “AA” often becomes the cause of nonviability. Astigmatism, hemeralopia, arachnodactyly are inherited.
  2. Incomplete dominance (intermediate type of inheritance). With heterozygosity, clinical manifestations are poorly expressed (for example, essential hypercholesterolemia); in the case of homozygosity, a pronounced form of pathology (for example, xanthomatosis).
  3. Autosomal recessive. The disease is phenotypically manifested in the case of the homozygote “aa”. This is how phenylketonuria, alkaptonuria, galactosemia are inherited.
  4. Inheritance due to sex chromosomes:
    1. through the homologous regions of the X- and Y-chromosomes the same in different sexes; pigmented xeroderma is inherited, spas-icy paraplegia;
    2. galandric inheritance (through non-homologous participation Y-chromosome current); diseases are transmitted from father to sons -hairiness of the ears, membranes between the fingers;
    3. through a non-homologous region of the X chromosome; are inherited recessive for women and dominant (due to hemizygotesnosti) for men, diseases – hemophilia, color blindness, ichthyosis;
    4. inheritance through plasmogenes – genes of the cytoplasm of the egg cells (for example, Leber’s syndrome – optic nerve atrophy).
  5. Multifactorial type of inheritance, in which there is a high variability in the relative role of genetic factors and the environment. It is noted in various chronic nonspecific diseases.

The frequency of hereditary diseases is determined by factors that introduce abnormal genes into the population or eliminate from it (for example, the mutational process and population migration).

Factors that shift the balance of gene frequencies are also important. Thus, consanguineous marriages lead to homozygotization of genotypes, are accompanied by degeneration and more frequent manifestation of hereditary diseases. The main types of selection that are significant for humans: selection against heterozygotes (for example, Rh-conflict between mother and fetus) and selection against homozygotes (sickle cell anemia and thalassemia).