Isochromosome

[1] Under normal separation of sister chromatids in anaphase, the centromere will divide longitudinally, or parallel to the long axis of the chromosome.

[1] A more common mechanism in the formation of isochromosomes is through the breakage and fusion of sister chromatids, most likely occurring in early anaphase of mitosis or meiosis.

[3] A double-stranded break in the pericentric region of the chromosome is repaired when the sister chromatids, each containing a centromere, are fused together.

[5] Misdivision of the centromere and U-type exchange can occur in sister chromatids, thus creating an isochromosome with genetically identical arms.

Since the p-arm of the X chromosome contains genes that are necessary for normal sexual development, Turner's syndrome patients experience phenotypic effects.

[7][8] Unique DNA sequences, known as low copy repeats, occur in the pericentric region of the p arm, so a crossover event in that area can create a dicentric isochromosome through U-type strand exchange.

The presence of one p53 gene can be functionally active, but its relation to other oncogenes can alter its expression levels when present only in one copy.

Isochromosome in which the arms are mirror copies of each other.
Isochromosome formation through the misdivision of the centromere. Monocentric isochromosomes contain arms that are mirror images of each other.