<prompt> What is the most impoant lesion produced in chromosomal DNA by exposure to ionizing radiation?A break on one DNA strand single-strand breakWell-separated breaks on both DNA strandsBreaks on both DNA strands which are opposite each other or separated by only a few bases double-strand breakMultiple breaks on the same DNA strand  <response>: In intact DNA, single strand breaks SSBs are of little biologic consequence because they are repaired readily using the opposite strand as a template. If the repair is incorrect misrepair, it may result in a mutation. If both strands of the DNA are broken and the breaks are well separated, repair again occurs readily, because the two breaks are handled separately.By contrast, if the breaks in the two strands are opposite one another or separated by only a few base pairs, this may lead to a double-strand break DSB; that is, the piece of chromatin snaps into two pieces. Double-strand breaks are the most impoant lesions produced in chromosomes by radiation.Reference: Eric J Hall Textbook of Radiobiology for Radiologist; 5th edition 