FISH "painting" patterns resulting from complex exchanges.

Many of the unusual patterns seen when irradiated chromosomes are FISH painted arise from Complex interchanges. In this paper, we present a method for classifying chromosome-type complex exchanges. Every possible exchange configuration for the first nine complex families has been determined, and for each of these, the expected metaphase pattern forms seen if any one of the participating chromosomes is painted, has been worked out. A total of 65 recognisably different pattern forms emerge, and a simple classification of these is provided for scoring and discussion purposes. 47 of these patterns are unique ("Tell-tale"), in that they are found in, and are diagnostic for, only one complex family or sub-family (of the sub-set analyzed). Analysis of the contingency tables indicates that: (a) The same individual complex exchange can appear in different pattern forms, depending upon which of the participating chromosomes is painted, and the converse-different forms can represent the same exchange. (b) Many different complex exchange configurations, from different families, can give rise to identical pattern forms. (c) If obvious complex forms are at all frequent in a sample, then a lot of the exchanges being scored as "simple" are not. These observations will have considerable repercussions on the numerical assessment of damage when using painted chromosomes at higher radiation doses.