Frequency of sister chromatid exchanges in a balanced reciprocal whole-arm translocation.

The frequency of sister chromatid exchanges (SCEs) in the centromere of chromosomes involved in a whole-arm translocation t(1:19) was evaluated in altogether 911 metaphases of translocation carriers (n = 5) and of normal controls (n = 6). Comparison of the two groups reveals no significant differences in the SCE rate (x2 = 3.06, nf = 1). The question as to whether the possible increase of the SCE rate at the translocation point could be detected by light microscopy is discussed. Parameters included in the discussion are the ratio of the SCE frequency at the translocation point to the SCE frequency at any of the possible breakage points in the centromeric region and the number of possible breakage points in the centromeric region.