Chromosomes experiencing delayed biorientation may be delayed as a result of syntelic attachment in both STLC washout and regularly cycling cells. (A and B) (A) Immunofluorescence of a monopolar spindle in wildtype PtK2 cells depicting a clear syntelic attachment (i) and a clear monotelic attachment (ii), unattached kinetochore denoted by arrowhead, and (B) a bipolar spindle following STLC washout again showing a clear example of a syntelic (i) attachment with kinetochore-microtubule attachment sites denoted by arrowheads. (C) Proportion of cells displaying either clear monotelic attachments, in which 1–3 kinetochores were clearly unassociated with microtubules, or no monotelic attachments in which kinetochores were all associated with microtubules (in either end-on or lateral configuration) in two independent experiments (left, right). In all cases of cells with monotelic attachment, cells displayed 1–3 unattached kinetochores, but never more. (D) Immunofluorescence of a wildtype, regularly cycling PtK2 cell highlighting a naturally occurring syntelic attachment with kinetochore-microtubule attachment sites denoted by arrowheads.