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.