View source for Etiology of chromosomal aberrations

===Chromosomal aberrations===
# Abnormalities in chromosome number
##aneuploidy
##*monosomy
##*trisomy (or tetrasomy, pentasomy...)
##polyploidy 
##*triploidy
##*tetraploidy,...
#Abnormalities in chromosome structure
##balanced
##*translocation
##*inversion
##*insertion
##unbalanced
##*deletion (incl. ring chromosome)
##*duplication
##*isochromosome

===Etiology of congenital chromosomal aberrations===
*Origin of aneuploidies and polyploidies (see question No. 34 – [[Abnormalities in chromosome number, their causes and clinical presentation in man|Abnormalities in chromosome number, their causes and clinical presentations in man]])
*Origin of structural aberrations:
**chromosome breaks and rearrangements during gamete formation (in meiosis) or in pre-gametic mitotic divisions of gonadal cells – resulting in stable products having one centromere and two telomeres 
***one centromere is necessary for regular segregation in mitosis (unstable dicentric chromosomes undergo secondary rearrangements)
***telomeres maintain the integrity of the ends of linear chromosome structure (in deleted chromosomes new telomeres are added by **telomere synthesis or by mechanism of telomere capture) 
**causes of spontaneous breaks – see below (external effects)

===Etiology of acquired chromosomal aberrations===
(= chromosome breaks and rearrangements during mitotic divisions of somatic cells)

External effects (physical, chemical, biological)
**random environmental factors – spontaneous breaks (UV light, ionizing radiation – cosmic rays, medical radiation (X-rays), drugs, viral infections)
**professional exposition (mutagens: chemicals – alkylating agents, intercalation substances...; radiation)
**oncological treatment (chemotherapy, radiotherapy)

'''Hereditary syndromes of chromosome instability''' 
*congenital defects of repair mechanisms - mostly double-strand DNA breaks repair
*rare genetic disorders with AR inheritance, higher predisposition to cancer development
*higher level of chromosome breaks and rearrangements detected in cytogenetic analysis
**ataxia teleangiectasia (defect of ATM gene - important for double-strand DNA breaks repair)
**xeroderma pigmentosum (defect of nucleotide excision repair)
**Bloom syndrome (extreme genome instability, high level of sister chromatid exchanges - SCEs, high frequency of mutations)
**Fanconi anemia
**Nijmegen breakage syndrome

Methods of analysis of acquired chromosomal aberrations (see question No. 31 – [[Methods of chromosomal examination]])

[[Category:Genetics]]