**8. Detection and analysis of preliminary chromosomal aberrations**

The primary chromosome aberrations could be detected and analysed in three forms such as achromatic lesions, chromosome type and chromatid type structural aberrations. The detection and characterization of aberrations or breaks which falls in the light banded region or euchromatic heterochromatin region which generally takes light stain could be identified as achromatic lesion. Chromosome type structural aberrations could be detected and identified in the form of asymmetrical interchanges (two translocations in the same arm), symmetrical interchanges (reciprocal translocations), inter arm intra changes (centric ring, pericentric inversions), intra arm intra changes (interstitial deletions, paracentric inversions), and breaks [(i) fragment compound (usually contains two terminal regions) and suspects an incomplete dicentric or centric ring; compound fragment with a terminal and unrelated non-terminal region suspects an incomplete complex interchanges, (ii) fragment simple (genetic material from one arm only) but with altered banding sequencing, suggest that sequence alteration is most frequently cause the inversion of a chromosomal proximal segment which is most probably indicates an incomplete paracentric inversion, (iii) fragment simple but the normal band sequence; (a) short arm with normal band sequences, if fragment present and not related to short arm might be incomplete reciprocal translocation or pericentric inversion; if fragment present and related to short arm may be true terminal deletion; (b) short arm with abnormal band sequences, first, observe for a distal inversion or incomplete paracentric inversion, second, observe for distal genetic

material missing or for incomplete interstitial deletions, third, observe for presence of any minutes and fourth, if any extra additional distal segment is present but not related to short arm with abnormal band sequences, it may be regarded as incomplete complex changes and look for the origin of additional segment, (iv) fragment simple but non terminal; perhaps represents incomplete acentric ring or large interstitial deletion]. Chromatid type structural aberrations could be detected and identified in the form of interchanges (involve the interchanges of chromatids), interarm intra changes (requires two breaks and causes pericentric inversions, double duplications-deletions, dicentric and centric rings), intra arm intra changes (two breaks involved and caused the formation of isochromatid deletion, duplication-deletion, chromatid minutes and paracentric inversions), and breaks [{causes chromatid terminal deletions and may be of various types; (i) a tandem duplication may be present in the complete chromatid, (ii) a tandem duplication may be present either in centric or acentric portion of the incomplete chromatid, (iii) the origin of acentric fragment may be of intercalary type and the sister chromatid has a normal pattern but it may show a bending opposite to the site of deletion, (iv) a paracentric inversion could be possible adjacent to the break in the acentric fragment but other sister chromatid may be normal, (v) a paracentric inversion could be possible adjacent to the break in the centric region or portion but other sister chromatid may be normal}].Additional chromatid type structural aberrations could be possible in the form of as isochromatid (isochromatid exchanges), insertions and additional dark bands in one of the chromatid at the exchange point. It is important to locate the position of aberration or break points at some stage in the production of breakage and rejoining of chromatid threads as this is the event that causes disruption and could be observed using different techniques. A detectable point of breakage is generally referred to as 'break point' but 'presumptive break point' would be more appropriate in light of consideration [40].

## **9. Mechanism of formation of chromosome aberration**

DNA breaks (especially dsDNA) is a serious threat for cell when unrepaired or misrepaired, as they can result in genomic instability or later on may lead to chromosomal alterations and even cell death. The chromosomal aberrations formation is one of the major alteration formed during dsDNA breaks. Moreover, it has been reported that during each cell division approximately 5000 ssDNA breaks were generated per nucleus and approximately 1% of total ssDNA breaks converted in dsDNA breaks. There were two theories forwarded for explanation of how chromosomal aberrations and its formation take place i.e. breakage and reunion theory and exchange theory. The breakage and reunion theory explains that breaks in chromosome may rejoin and form the original structure through restitution and the exchange theory might lead to exchange the aberration by rejoining another type of breaks. dsDNA breaks could be repaired by possibly three pathways i.e. homologous recombination repairing (HRR) which restores the original sequences, non-homologous DNA end joining (NHEJ) which usually generates and repairs small alterations such as base pair substitution, insertions, deletions at break sites etc., and single strand annealing (SSA) which may lead to the formation of interstitial deletions. HRR (requires one break) and NHEJ (requires two breaks) and SSA are important pathways for repairing of dsDNA breaks with one or two breaks in eukaryotic cells as well as mammalian cells [41].

Chromosomal aberrations may be caused by various physical and chemical factors such as ionizing radiations, chemicals and spontaneous dsDNA breaks e.g. endogenous reactive oxygen species, topoisomerases and replication errors.

**57**

**Author details**

**10. Conclusion**

Sanjay Kumar1

\*, Asikho Kiso2

provided the original work is properly cited.

mental and synthetic chemicals.

and N. Abenthung Kithan2

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Department of Botany, Banaras Hindu University, Varanasi, India

2 Department of Botany, Nagaland University, Nagaland, India

\*Address all correspondence to: ksanjay79@gmail.com

*Chromosome Banding and Mechanism of Chromosome Aberrations*

There are various methods for the detection of chromosomal aberrations such as cytogentic testing [{(a) chromosomal aberration test, (b) micronucleus test; (i) giemsa staining method, (ii) cytokinesis-blocked micronucleus assay method, and (iii) flow-cytometry micronucleus assay method, (c) karyotyping}], molecular cytogentic testing [(a) fluorescence in situhybridization (FISH), (b) microarray comparative genomic hybridization (mCGH)], and prenatal screening to

The clinical symptoms of chromosomal aberrations includes, a) chromosomal aberrations and spontaneous aberrations (e.g. congenital malformations, heart and renal malformations), b) chromosomal aberrations and cancer (e.g. chronic myeloid leukemia), c) behaviour peculiarities associated with chromosomal aberrations (e. g. turner syndrome), d) changes in course of adolescence and fertility (e.g. premature aging), e) pattern of dysmorphic signs in chromosomal aberrations (e.g. down syndrome, cri-du-cat syndrome) and f) congenital malformations and chromosome aberrations (e.g. dandy-walker malformation, gastrointestinal

At present, most of the studies are surrounded towards the human health and disease caused by the interaction of genetic and environmental factors. Sometimes it is difficult to understand the genetic constitution or mechanism of chronic diseases. Therefore, it is very important to understand the mechanism behind the abnormal cells either genetic or environmental or both to solve the problems completely. The identification of a particular abnormality at the initial stage is crucial and banding techniques conventional or molecular provide such an opportunity. Banding and chromosome aberrations are played an important key role in the assessment of various risks faced by the genetic constitution of eukaryotic cells. Therefore, it may continue further to assess the risk of various kinds of ailments, diseases, and geno-toxicity induced by the radiations, pharmaceuticals, environ-

*DOI: http://dx.doi.org/10.5772/intechopen.96242*

detect foetal abnormalities [42].

malformations, CNS-spina bifida) [43].

*Chromosome Banding and Mechanism of Chromosome Aberrations DOI: http://dx.doi.org/10.5772/intechopen.96242*

There are various methods for the detection of chromosomal aberrations such as cytogentic testing [{(a) chromosomal aberration test, (b) micronucleus test; (i) giemsa staining method, (ii) cytokinesis-blocked micronucleus assay method, and (iii) flow-cytometry micronucleus assay method, (c) karyotyping}], molecular cytogentic testing [(a) fluorescence in situhybridization (FISH), (b) microarray comparative genomic hybridization (mCGH)], and prenatal screening to detect foetal abnormalities [42].

The clinical symptoms of chromosomal aberrations includes, a) chromosomal aberrations and spontaneous aberrations (e.g. congenital malformations, heart and renal malformations), b) chromosomal aberrations and cancer (e.g. chronic myeloid leukemia), c) behaviour peculiarities associated with chromosomal aberrations (e. g. turner syndrome), d) changes in course of adolescence and fertility (e.g. premature aging), e) pattern of dysmorphic signs in chromosomal aberrations (e.g. down syndrome, cri-du-cat syndrome) and f) congenital malformations and chromosome aberrations (e.g. dandy-walker malformation, gastrointestinal malformations, CNS-spina bifida) [43].
