A ring chromosome is an aberrant chromosome whose ends have fused together to form a ring. Ring chromosomes were first discovered by Lilian Vaughan Morgan in 1926. A ring chromosome is denoted by the symbol r in human genetics and R in Drosophila genetics. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, but they may also arise spontaneously during development.
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.
Lilian Vaughan Morgan was an American experimental biologist who made seminal contributions to the genetics of the fruit fly Drosophila melanogaster, although her work was obscured by the attention given her husband, Nobel laureate Thomas Hunt Morgan. Lilian Morgan published sixteen single-author papers between 1894 and 1947. Probably her most significant scientific contribution was the discovery of the attached-X chromosome and an entirely new pattern of inheritance in Drosophila in 1921. She also discovered the closed or ring-X chromosome in 1933. Both are important research tools today.
Lilian Vaughan Morgan
