Bivalent

bivalent
The complex formed by a pair of homologous chromosomes during meiosis I.
Source: Jenkins, John B. 1990. Human Genetics, 2nd Edition. New York: Harper & Row ...

Bivalent
A pair of homologous chromosomes closely adjacent to each other formed during the first meiotic division within a primary spermatocyte or oocyte.

During the prophase of meiosis I, homologous chromosomes pair and form synapses. The paired chromosomes are called bivalents. The bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.

Bivalent A pair of homologous chromosomes closely associated in prophase and metaphase of the first meiotic division.

Bivalent a pair of homologous chromosomes during meiosis‚ also known as a tetrad
(bi = two; valent = strength)
Blastocyst the hollow ball stage of embryonic development
(blasto = bud‚ sprout) ...

Bivalents, each composed of two chromosomes (four chromatids) align at the metaphase plate. The orientation is random, with either parental homologue on a side.

Bivalents (tetrads) become aligned in the center of the cell and are attached to spindle fibers.
The chromosome alignment illustrated below is from a cell with a diploid chromosome number of 8.
...

bivalent The pairs of homologous chromosomes at synapsis in the first meiotic division, a tetrad.
bivalves The clams, mussels, and other molluscs that possess a two-valved shell, filtering gills, and a shovel-like foot.

Chromosomes of bivalents pulled to opposite poles at random
2n different combinations of chromosomes in four haploid cells produced where n is the haploid number of chromosomes
Crossing over between non-sister chromatids during prophase I ...

Bipolar cells of human retina Birds Birth control Birth, human Biston betularia Bivalent Bivalvia Blastema BlastocystThe blastula formed by placental mammals. The blastocyst is the embryonic stage that implants in the wall of the uterus.

You know, I was ambivalent. I had assumed that, when Frank died, that I would also follow suit soon. I never expected to see the year 1985. I certainly never expected to see the year 2000.

plate: as kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align along an equatorial plane that bisects the spindle, due to continuous counterbalancing forces exerted on the bivalents ...

Chiasma interference: the more frequent (in the case of negative chiasma interference) or less frequent (in the case of positive interference) occurrence of more than one chiasma in a bivalent segment than expected by chance.

The chromosomes formed almost no bivalents during meiosis. Artificially doubling the chromosome number using colchecine produced a hexaploid hybrid which closely resembled M. citrigracilis and was fertile.

See also: Chromosomes, Chromosome, Homologous chromosomes, Homologous chromosome, Meiosis