Distribution and relation of radiation induced chromosomal aberrations in human lymphocytes as seen in the first and second cell cycles.

Different types of chromosomal damage in the G(o) phase of human lymphocytes have been studied in the first (M1) and second cell lymphocytes (M2). Large populations of cells containing one dicentric chromosome and one acentric (DIC+) were observed in the second cycle. This indicates that these dicentric and acentric fragments have a normal distribution in M2 or, arose through loss of one acentric fragment (AC) from cells containing one dicentric and two acentric fragments (DIC++) in M1. Similarly, a large number of metaphases in M2 have unpaired differentiated ACs. Our data indicates that aberrant metaphases containing single AC or a DIC+ may undergo normal cell division and that these cells may not represent cells in the first cycle only, as was suggested by earlier workers. For radiation experiments to G(o), a desirable time to harvest human lymphocyte cultures appears to be 72 hours and screening of M1 and M2 cells by sister chromatid differentiation.