Bivalents


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Bivalents

 

pairs of connected (conjugated) homologous chromosomes formed during nuclear division in meiosis. Chiasmas—X-shaped figures—are formed between chromosomes; they hold the chromosomes together within the complex. Genetic material may be exchanged at this time. The number of bivalents is normally equal to the number of chromosomes of the haploid (single) set.

References in periodicals archive ?
In diplotene/diakinesis some the autosomal bivalents shows telomeric associations (Fig.
Notably, one year after the publication of Carother's 1931 paper, Darlington (1932) correctly interpreted her images of heteromorphic bivalents and established that first division is reductional with respect to the centromere and the region between it and the first chiasma, while the portion distal to the chiasma undergoes equational segregation (Darlington 1958, Hegreness & Meselson 2007).
The meiotic analysis of Aster squamatus showed 10 chromosomes in bivalent associations (II) in diakinesis and metaphase 1 (Figure 1a), normal chromosomal segregation in anaphase 1 (Figure1b) and telophase 1, and retarding chromosomes in telophase II (Figure 1c), as well as cells with 3 poles (Table 1), and one cell with 5 (Figure 1d).
The frequency of univalents, bivalents, trivalents, and quadrivalents were determined in at least 10 microspore mother cells (616 total) from each of 50 euploid plants at metaphase I.
In those individuals heterozygous only for fission of chromosome 6 (the smallest Robertsonian chromosome), the elements of the trivalent often completed synapsis before the larger autosomal bivalents (i.
Ditactic bivalents were first described in species of the genus Stethophyma by McClung (1928), who believed they resulted from cases in which chiasmata are only confined to the short arms of acrocentric chromosomes, an opinion which was held and reiterated by White (1951, 1973).
Meiosis is achiasmatic; all bivalents are homomorphic, condensing gradually until metaphase I (Fig.
Usually, when m chromosomes are present, the X and Y form part of the ring of the autosomal bivalents at first metaphase, and the m pseudobivalent lies in its centre.
Unequal crossing over and heterochromatin exchange in the X-Y bivalents of the deer mouse, Peromyscus beatae.
All bivalents present a ring shape, evidencing the occurrence of two terminal chiasmata per bivalent, and the X chromosome constitutes an univalent during all meiosis I (Fig.