<P> Errors can occur during mitosis, especially during early embryonic development in humans . Mitotic errors can create aneuploid cells that have too few or too many of one or more chromosomes, a condition associated with cancer . Early human embryos, cancer cells, infected or intoxicated cells can also suffer from pathological division into three or more daughter cells (tripolar or multipolar mitosis), resulting in severe errors in their chromosomal complements . </P> <P> In nondisjunction, sister chromatids fail to separate during anaphase . One daughter cell receives both sister chromatids from the nondisjoining chromosome and the other cell receives none . As a result, the former cell gets three copies of the chromosome, a condition known as trisomy, and the latter will have only one copy, a condition known as monosomy . On occasion, when cells experience nondisjunction, they fail to complete cytokinesis and retain both nuclei in one cell, resulting in binucleated cells . </P> <P> Anaphase lag occurs when the movement of one chromatid is impeded during anaphase . This may be caused by a failure of the mitotic spindle to properly attach to the chromosome . The lagging chromatid is excluded from both nuclei and is lost . Therefore, one of the daughter cells will be monosomic for that chromosome . </P> <P> Endoreduplication (or endoreplication) occurs when chromosomes duplicate but the cell does not subsequently divide . This results in polyploid cells or, if the chromosomes duplicates repeatedly, polytene chromosomes . Endoreduplication is found in many species and appears to be a normal part of development . Endomitosis is a variant of endoreduplication in which cells replicate their chromosomes during S phase and enter, but prematurely terminate, mitosis . Instead of being divided into two new daughter nuclei, the replicated chromosomes are retained within the original nucleus . The cells then re-enter G and S phase and replicate their chromosomes again . This may occur multiple times, increasing the chromosome number with each round of replication and endomitosis . Platelet - producing megakaryocytes go through endomitosis during cell differentiation . </P>

In which mitotic phase do the chromosomes condense and does the mitotic spindle begin to form