| sister chromatid exchange | An aberrant crossing-over event in which there is an exchange of segments 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. It can be induced by ultraviolet and ionizing radiation or by mutagenic agents and is observed by autoradiography. (12 Dec 1998) |
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| Sister Joseph's nodule | A malignant intra-abdominal neoplasm metastatic to the umbilicus. (05 Mar 2000) |
| Sister Mary Joseph Dempsey | Superintendent at Saint Mary's hospital, Mayo Clinic, and surgical assistant to Dr. William Mayo, c. 1928, 1856-1929. See: Sister Joseph's nodule. (05 Mar 2000) |
| sisterhood | 1. The state or relation of being a sister; the office or duty of a sister. "She . . . Abhorr'd Her proper blood, and left to do the part Of sisterhood, to do that of a wife." (Daniel) 2. A society of sisters; a society of women united in one faith or order; sisters, collectively. "A sisterhood of holy nuns." "The fair young flowers . . . A beauteous sisterhood." (Bryant) Origin: Sister + hood. Source: Websters Dictionary (01 Mar 1998) |
| Sistrunk | Walter Ellis, U.S. Surgeon, 1880-1933. See: Sistrunk operation. (05 Mar 2000) |
| Sistrunk operation | Excision of the thyroglossal cyst and duct including the midportion of the hyoid bone through, or near, which the duct traverses. (05 Mar 2000) |
| sisyphus | A king of Corinth, son of aeolus, famed for his cunning. He was killed by Theseus, and in the lower world was condemned by Pluto to roll to the top of a hill a huge stone, which constantly rolled back again, making his task incessant. Origin: L. Sisyphus, Sisyphus, fr. Gr. Source: Websters Dictionary (01 Mar 1998) |