| 释义 |
univalent, a. and n. Chem.|juːnɪˈveɪlənt, juːˈnɪvələnt|
[f. uni- + L. valent-em, pr. pple. of valēre to be worth.]
A. adj.
1. Having a valency of one; having the combining power of one atom of hydrogen or other radical.
Also, in recent Dicts. (1891–), univalence, univalency.
1869Eng. Mech. 19 Nov. 222/1 A univalent body can only join its single atom to a single atom of a univalent body. 1872Watts Dict. Chem. VI. 243 Chlorine is univalent in argentic chloride. 189319th Cent. Aug. 249 Each atom of potassium..is univalent, and has the same valency as one atom of hydrogen.
2. Cytology. |juːˈnɪvələnt|. [ad. mod.L. univalens (introduced in Ger. by O. Hertwig 1890, in Arch. f. mikrosk. Anat. XXXVI. 6).] Of a chromosome: remaining unpaired during meiosis. Cf. monovalent a. 3.
1898Zool. Jahrb. (Abt. für Anat.) XII. 79 The chromosomes of the 1st reduction division are univalent, when they occur in the normal number. 1916Jrnl. Morphol. XXVII. 226, I believe he [sc. Haecker] is wrong in thinking that the ‘univalent’ chromosomes making up these ‘bivalents’ are to be considered as members of homologous chromosome pairs. 1971Nature 19 Feb. 570/2 Many authors have reported that the behaviour of univalent chromosomes at meiosis is irregular. 1981Jrnl. Cell Biol. LXXXVIII. 281 During meiosis I in males of the mole cricket Neocurtilla (Gryllotalpa) hexadactyla, the univalent X1 chromosome and the heteromorphic X2Y chromosome pair segregate nonrandomly.
3. Immunol. = monovalent a. 2 b.
1939Bacteriol. Rev. III. 76 If Hooker and Boyd now believe antibody to be univalent they must abandon the entire basis for these and other of their calculations. 1940Jrnl. Exper. Med. LXXI. 271 Antibody is referred to as low grade, incomplete, imperfect, or ‘univalent’ in instances in which it is incapable by itself of precipitating with added antigen. 1977M. W. Steward in Glynn & Steward Immunochemistry vii. 245 There are several reports which show the reduction in neutralization of both animal viruses..and bacteriophages..when univalent antibodies have been used.
B. n. Cytology. |juːˈnɪvələnt|. A univalent chromosome.
1912Jrnl. Exper. Zool. XIII. 350 In the first division the X- and Y-chromosomes divide as separate univalents. 1921Ann. Bot. XXXV. 173 These chromosomes were of two types, as revealed during meiosis, fourteen being bivalents and twenty-one univalents. 1971Nature 19 Feb. 570/2 In the triploid species Leucopogon juniperinus univalents are close to the poles at metaphase, but..they are not in the same plane as the spindle on which the bivalents are positioned. |