bivalent

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Related to bivalents: bivalent chromosome

bivalent

 [bi-va´lent]
the structure formed by a pair of homologous chromosomes joined by synapsis along their length during the zygotene and pachytene stages of the first meiotic prophase. After each homologous chromosome splits into two sister chromatids during the pachytene stage, this structure is called a tetrad.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

bi·va·lent

(bī-vā'lent, biv'ă-lent),
1. Having a combining power (valence) of 2.
See also: tetrad. Synonym(s): divalent
2. In cytology, a structure consisting of two paired homologous chromosomes, each split into two sister chromatids, as seen during the pachytene stage of prophase in meiosis.
See also: tetrad.
Farlex Partner Medical Dictionary © Farlex 2012

bivalent

(bī-vā′lənt)
adj.
1. Genetics Relating to or being a pair of homologous, side-by-side chromosomes, especially during meiosis; double.
2. Chemistry & Immunology Divalent.

bi·va′lence, bi·va′len·cy n.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

bivalent

Chemistry
adjective Referring to an atom with 2 valent states.
 
Genetics
adjective Referring to either of 2 homologous chromosomes in synapsis during meiosis.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

bi·va·lent

(bī-vā'lĕnt)
1. Having a combining power (valence) of two.
Synonym(s): divalent.
2. cytology a structure consisting of two paired homologous chromosomes, each split into two sister chromatids, as seen during the pachytene stage of prophase in meiosis.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

bivalent

(of a pair of homologous CHROMOSOMES) being paired during prophase I of MEIOSIS. Compare MULTIVALENT.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
Seventy-five percent of bivalents were rod bivalents.
Jenkins and Jimenez (1995) suggested B chromosomes appear to promote bivalent formation in the Lolium amphiploids.
Cytogenetically, the differences between the pre-reductional and post-reductional meiosis are characterized by the orientation of the bivalents (White 1973).
The Structure of Bivalents in the Homoptera Auchenorrhyncha.
Therefore, we arrive at an apparent paradox, because the effective recombination in this species occurs mainly in nonpericentromeric regions of female bivalents. In grasshoppers, the lack of a clear tendency in patterns of chiasma frequency and in distribution differences between sexes, even between related species, makes it difficult to envisage the possible adaptive value of these changes in the recombination patterns (Cano & Santos 1990).
In the studied accessions from Pterocaulon polystachyum (Table 1), the following were observed: 9 bivalent chromosomes (II) in diakinesis and metaphase 1 (Figure 1e, 1f), and normal chromosomal segregation in anaphase and telophase I and II (9-9), even though some irregularities occurred, like a telophasic bridge (Figure 1g) and a retarding chromosome in one cell.
Because of the necessity for a minimum of one crossover per bivalent, smaller chromosomes experience higher recombination rates than larger chromosomes (Kaback et al., 1992, and references therein).
2b, 3a); meiosis is achiasmatic, and bivalents are homomorphic, condensing gradually during prophase I (Figs.
Chromosome associations([dagger]) Cells Frequency % 1 IV + 13 III + 6 II + 6 I 1 2.5 1 IV + 12 III + 7 II + 7 I 2 5.0 I IV + 11 III + 8 II + 8 I 1 2.5 18 III + 3 II + 1 I 1 2.5 16 III + 4 II + 5 I 2 5.0 15 III + 6 II + 4 I 1 2.5 14 III + 7 II + 5 I 1 2.5 14 III + 6 II + 7 I 1 2.5 13 III + 8 II + 6 I 3 7.5 13 III + 6 II + 10 I 1 2.5 12 III + 9 II + 7 I 2 5.0 12 III + 8 II + 9 I 1 2.5 11 III + 11 II + 6 I([double dagger]) 1 2.5 11 III + 10 II + 8 I 4 10.0 11 III + 9 II + 10 I 3 7.5 10 III + 11 II + 9 I 5 12.5 9 III + 13 II + 8 I([double dagger]) 1 2.5 9 III + 12 II + 10 I 4 10.0 8 III + 13 II + 11 I 2 5.0 7 III + 14 II + 12 I 2 5.0 5 III + 15 II + 16 I 1 2.5 Total 40 ([dagger]) Chromosome associations: IV = quadrivalents, III = trivalents, II = bivalents, I = univalents.