MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.2. Basics of Human Genetics

Mutational Variability, Classification of Mutations

A mutation is a sudden, discrete change in a hereditary trait caused by an alteration of the genetic material. Mutagenesis is The process of mutation occurrence. A mutant is an Organism that has changed its phenotype As a result of a mutation. Mutations were first described in the evening primrose (Oenothera lamarckiana) and the term was introduced into science by the Dutch botanist H. de Vries (1901), one of the three scientists who rediscovered the laws of inheritance established by G. Mendel. Evolution—the process of forming new species, varieties, and breeds—is closely associated with mutational variability. Mutations are known in all classes of animals, plants, and Viruses. It is mutations that account for the polymorphism of human populations: varying Skin pigmentation, Hair and eye color, shape of the Nose, Lips, etc. Clinically, mutations manifest as Hereditary diseases.

Unlike modifications:

1. Mutations arise suddenly and discontinuously, without transitional states compared to the initial form of the trait.

2. New traits are stable and inherited across a series of generations.

3. They are qualitative, discrete changes; they do not form continuous series and do not cluster around the mean value of a trait.

4. Mutations occur in various directions and may arise repeatedly.

5. They are individual in nature, meaning they appear in any single individual that exists under the same environmental conditions as other individuals of the same species.

6. Mutations are not adaptive to environmental factors and generally lack adaptive value.

There are several classifications of mutations. According to their origin, mutations are divided into Spontaneous and Induced. Spontaneous (natural) mutations occur in natural conditions without the intervention of an experimenter. Their frequency is low, and the causes are undetermined. Induced (artificial) mutations occur when an organism is exposed to specific factors. Their frequency is several orders of magnitude higher than that of spontaneous ones. Mutations can occur in both somatic (somatic mutations) and germ (generative mutations) Cells. Based on their cellular localization, nuclear mutations (occurring in the Chromosomes of the Cell Nucleus) and cytoplasmic mutations (occurring in cytoplasmic Organelles that have their own DNA, such as Mitochondria and Plastids) are distinguished. According to the nature of changes, mutations are subdivided into morphological, physiological, and biochemical. Regarding their effect on viability,

mutations are classified as beneficial, harmful, and neutral. Most mutations are harmful. Among them are lethal, sublethal, and conditionally lethal mutations. Lethal mutations are incompatible with life; they cause the death of the organism before birth. Sublethal mutations reduce the organism's viability, leading to its death in the period from birth to Puberty. Conditionally lethal mutations exhibit a lethal effect under certain conditions. Depending on the direction, mutations can be forward or reverse. Forward mutations convert the wild-type (normal) allele into a mutant one (A → a), while reverse mutations restore the mutant allele to the initial type (a → a). The process of reverse transition is called reversion. Based on The amount of genetic material involved in the Mutational Process, mutations are divided into major (macromutations) and minor (micromutations). According to the level of Organization OF THE genetic material, genomic, chromosomal, and Gene Mutations are distinguished.