[An exchange of homologous segments of genetic material between the sister chromatids of a chromosome, either between the sister chromatids of a meiotic tetrad or between the sister chromatids of a duplicated somatic chromosome. Its frequency is increased as a result of inordinate chromosomal fragility due to genetic or environmental factors such as ultraviolet or ionizing radiation and other mutagenic agents, and is particularly high in Bloom Syndrome. ( NCI )]
UMLS (CSP) C0037211