Medical Genetics - V. M. Zaporozhan 2005

Etiology of Hereditary Diseases
Mutagenic Factors
Physical Mutagens

Environmental factors capable of triggering Mutations are referred to as Mutagenic Factors, or mutagens. Many mutagens are also carcinogens, meaning they can induce mutations in genes responsible for malignant growth. Depending on their origin, mutagens are classified into physical, chemical, and biological factors.

Physical mutagens include all Types of ionizing radiation (X-rays, u-rays, neutron and proton radiation, etc.), ultraviolet rays, elevated temperatures, and others. Ionizing radiation causes various alterations in genetic material associated with breaks and rearrangements in individual Chromosomes and DNA molecules, Modification of the chemical Structure of NUCLEOTIDES, and other damage. The mutation frequency is directly proportional to the dose of X-ray irradiation. Furthermore, it should be noted that ionizing radiation has no minimum threshold dose, meaning that even a minor exposure can disrupt The structure of DNA. The Effect of ionizing radiation is cumulative in nature (chronic exposure to low doses leads to a gradual accumulation of mutations over time).

Table 2.5. Symbols used to designate chromosomal mutations (after E. K. Ginter, 2003)

Symbol

Type of mutation

Karyotype notation example

del

Deletion

46,XX, del (5р) — deletion of the short arm of chromosome 5 (cri du chat syndrome) in a female

dup

Duplication

46,XY, dup (11) (q12) — male karyotype with duplication of segment q12 of chromosome 11

i

Isochromosome

46,Х, i (Xq) — isochromosome for the long arm of X in a female, the second X chromosome is normal

inv

Inversion

46,XY, inv(10) (р 13q12) — male karyotype, pericentric inversion with breakpoints p13 and q12

rob

Robertsonian

translocation

45,ХХ, rob (14q21q) — female with a balanced Robertsonian translocation of the long arms of chromosomes 14 and 21

46,ХХ, -14,+rob (14q21q) — female with an unbalanced Robertsonian translocation, chromosome 14 is not identified in the karyotype, + translocation chromosome

r

Ring chromosome

46,XY, r(18) — ring chromosome 18 in a male

t

Translocation

46,ХХ, t (2;4) (q21; q21) — female with a reciprocal translocation involving the long arm of chromosome 2 starting from segment 2q21 and the long arm of chromosome 4 starting from segment 4q21

fra

Fragile site

46,XY, fra (Х) (q27.3) — male with a fragile site on the long arm of the X chromosome, detected in fragile X syndrome

Unlike ionizing radiation, ultraviolet rays do not penetrate deep into Tissues; therefore, mutations induced by them affect only the Cells of superficial tissues.



Last update: 11/08/2026

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