Ring chromosome

Ring chromosomes may form in cells following genetic damage by mutagens like radiation, but they may also arise spontaneously during development.

In rare cases, the telomeres at the ends of a chromosome fuse without any loss of genetic material, which results in a normal phenotype.

[2] Complex rearrangements, including segmental microdeletions and microduplications, have been seen in numerous ring chromosomes, providing important clues regarding the mechanisms of their formation.

[4] Human genetic disorders can be caused by ring chromosome formation.

[5] Location of fusion also affects severity due to loss of differing amounts of genetic material from the ends of chromosomes.

Representative karyotype from a well differentiated transitional cell carcinoma of the bladder. The chromosome indicated by "mar" represents unidentified marker, "r" represents ring chromosome. Arrowheads indicate breakpoints. Also evident are monosomy 9, 18, and X and trisomy 7.
Formation of a ring chromosome.