Sister chromatid exchanges in a ring chromosome 4

Translocation of chromosome 4 and 9 with ring formation of chromosome 4 short arm.

“…The ring 4 chromosomes described by Hecht (1969), Carter et al (1969), Faed et al (1969), and Parker et al (1974) have all shown evidence of instability leading to missegregation with resultant mosaicism, breakage, and polycentric ring formation by sister chromatid exchange (Hecht, 1969). However, Bartram (1977) did not observe any increase in sister chromatid exchanges in a ring 4 chromosome investigated after 2 replication cycles in the presence of BrdU. These dicentric and tetracentric rings may undergo breakage and reunion at anaphase leading to rings of unequal size.…”