output_of merotelic kinetochore attachment during mitosis mitotic spindle collapse during anaphase B elongation mitotic spindle collapse during anaphase B elongation with progressive spindle pole congression A cell phenotype in which a mitotic spindle assembles and begins to elongate, but collapses during anaphase B, with the collapse being followed by the spindle poles congressing together. In some cases, this is known to be driven by depolymerisation of microtubules part of a merotelic attachment (PMID:19948483).