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.

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.

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.

bivalent

Chemistry
adjective Referring to an atom with 2 valent states.
 
Genetics
adjective Referring to either of 2 homologous chromosomes in synapsis during meiosis.

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.

bivalent

(of a pair of homologous CHROMOSOMES) being paired during prophase I of MEIOSIS. Compare MULTIVALENT.
References in periodicals archive ?
True bugs, the Heteroptera, have many cytogenetic characteristics that make them unique among most insect groups: the possession of chromosomes without a primary constriction, the centromere, namely holokinetic chromosomes; a pair of <<m chromosomes>> in 16 families, belonging to four infraorders; a different meiotic behaviour for autosomes and sex chromosomes; and a mean chiasma frequency of only one chiasma per bivalent (Ueshima, 1979; Nokkala, 1986; Papeschi & Bressa, 2006).
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.