As our DNA or any other kingdom's or species' DNA is made by same kind of chemistry i strongly believe the DNA repair capacity matters and have a great effect on genomic integrity. The strand breaks (single or double- if they are not repaired) of DNA can be visualized as Chromatid Breaks in the metaphase (by observing Chromosomes). There are lot of publications which can interpret the possibility of gaps and breaks in the chromosome arms (Chromatids) !

1) On the nature of visible chromosomal gaps and breaks. 2004) Savage JR. Cytogenet Genome Res. 104(1-4):46-55.

The above article is just an introduction, if your question concentrates on how the chromatid break happens .?

The damage to the human genome incurs on the order of 1, 000-1,000,000 DNA lesions/cell/day ( Molecular Cell Biology by Harvey Lodish, 4th edition 2000) Most of the lesions are caused by endogenous sources, including reactive oxygen and nitrogen species (ROS, RNS) that can oxidize cellular macromolecules including lipid, protein and nucleic acid where one or the other takes part in the integrity of genome and DNA damage signals

"in common man's words' ...for example..... what does affect the normal cell.?"

the lymphocytes can be affected by the air u breath in

Skin can be affected by the sun light u get exposed

squamous cells in the the passages of the respiratory and digestive tracts, and the linings of the hollow organs of the body can be affected by the HOT DRINKS you take and the SMOKE u inhale.. and they get repaired...this is all normal stories Check out the below article it might be useful

2) Schanz S , Flockerzi E, Schuberth K, Rübe CE (2014) Genetically-Defined DNA Repair Capacity Determines the Extent of DNA Damage Accumulation in Healthy Mouse Tissues after Very Low Doses of Ionizing Radiation. J Carcinog Mutagen 5:196. doi: 10.4172/2157-2518.1000196 good luck!

what a great information, thank you so much Mr. Alex George

Alex

Don´t forget chronic inflammatory processes,     or   environmental policiclic  aromatics hydrocarbons  that in dependence of the kind of facility   where mice are caged, can reach mice respiratory tract. Several environment agents along with the aforementioned metabolicaly originated   caused  base modifications  that can trigger DNA repair mechanisms like short or long patch BER , or NER  among other that generates damage that can be expressed as chromatids gaps or breaks according to  the moment in cell cycle  when lesions are produced

Dear Husni Mubarok,

I suggest reading J Carcinog Mutagen 5:196. doi: 10.4172/2157-2518.1000196 

There are several factors causing chromatid breaks in natural conditions: i) replication across a nick would give rise to chromatid breaks; ii) a second cause is oxidation from radicals occurring during normal oxidative respiration; iii) failures of DNA  topoisomerases; and  iv) natural ionizing radiation including gamma rays and X-rays.

Thank you Mr. Daniel Lerda and Mr. Amadeu Creus

I have a lot of informations from all of you :)