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the four homologous chromatids in a bundle during the prophase and metaphase of meiosis
Source: Jenkins, John B. 1990. Human Genetics, 2nd Edition. New York: Harper & Row ...

Groups of four. At metaphase of meiosis, chromosomes are grouped in pairs. We can therefore count four chromatids. This is why this arrangement is called a tetrad.
View Dr Chromo's lecture on 'Meiosis'.
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Tetrad analysis
A method for establishing linkage relationships in fungi by analysing the four products from individual meiotic divisions.
The four products of a single meiosis.

[Gk. tetras, four]
In genetics, a pair of homologous chromosomes that have replicated and come together in prophase I of meiosis; consists of four chromatids.
tetrapod ...

tetrad The four chromatids in each cluster during synapsis; formed by the two sister chromatids in each of the two homologous chromosomes. PICTURE ...

~ - Chromosome complex formed by the synapsis of homologous chromosomes during meiotic prophase I. A ~ contains four chromatids.

the four homologous chromatids that associate during prophase and metaphase of meiosis and are involved in crossing over. A ~ is also the four haploid cells produced by one complete meiotic division.
Covered in BIOL1020 Lab 6 Mitosis & Meiosis ...

~ analysis
When diploid S. cerevisiae cells undergo meiosis, four haploid spores are produced which are enclosed within a sac called an ascus. Using a micromanipulator, the 4 spores (the "~") can be "dissected" out of the ascus and separated on an agar plate.

Half-~ genetic mapping of centromeres
Centromere positions were mapped using half-~ analysis in a population of 49 plants derived from first-division restitution unreduced gametes of several B. napus - B. carinata hybrids [37]. A total of 13,098 SNPs polymorphic between the B.

The four haploid cells formed at the end of meiosis. The term was formerly used for the four chromatids making up a chromosome-pair at the first division of meiosis.
Related Terms:
Haploid ...

~ A pair of homologous chromosomes during synapsis (prophase I of meiosis). A ~ consists of four chromatids.
tetrapods A nontaxonomic designation used to refer to amphibians, reptiles, birds, and mammals.

Each ~ is comprised of four chromotids - the two homologs, each with their sister chromatid
Homologous chromosomes will swap genetic material in a process known as crossing over (abbreviated as XO)
Crossing over serves to increase genetic diversity by creating four unique chromatids ...

In reality, however, the number is doubled, since each chromosome consists of four granules grouped to form a ~.

Result: a ~. (These structures are sometimes referred to as bivalents because at this stage you cannot distinguish the individual sister chromatids under the microscope.)
The two homologous dyads are held together by ...

This may occur if ~ chromosomes do not separate properly during meiosis I.
Alternatively, sister chromatids may fail to separate during meiosis II.

Recent advances, including whole-genome sequencing efforts, chromatin immunoprecipitation using kinetochore proteins, and ~ analysis in the model plant Arabidopsis thaliana, have bolstered the belief that centromere satellite repeats may be functionally important sequences [5-8].

Prophase I: Dyad pairs align to create "~S", non-sister chromatids connect and trade sections at a "CHIASMA", a process called "CROSSING OVER".
Metaphase I: SPINDLE FIBERS attach to each dyad at the KINETOCHORE. Tension from spindle fibers aligns the ~s at the cell equator.

crossing over a process during prophase I in which segments of DNA from one chromatid in the ~ pass to another chromatid in the ~.
cyanobacteria see blue-green algae.
cytochromes molecules that accept and release electrons in an electron transport system.

:30 This is the first point in meiosis where the four parts of the ~s are actually visible. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible.

Some of these Hsp100 chaperones, like ClpA and ClpX, associate with the double-ringed ~ecameric serine protease ClpP; instead of catalyzing the refolding of client proteins, these complexes are responsible for the targeted destruction of tagged and misfolded proteins.
[edit] History ...

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

A cross-shaped structure commonly observed between nonsister chromatids during meiosis; the site of crossing-over. X-shaped configuration seen in ~s during the latter stages of prophase 1 of meiosis. They represent physical crossovers between DNA molecules.

bivalent /BUY-vale-ənt/ n. A pair of synapsed homologous chromosomes; this configration occurs during meiotic prophase I. Also known as a "~."
bivalved /BUY-valvd/ adj. Having a pair of hard shells that open for feeding and close for protection.

AP-1 is actually a complex between c-fos protein and c-jun protein, or sometimes is just c-jun dimers. The AP-1 site consensus sequence is (C/G)TGACT(C/A)A. Also known as the TPA-response element (TRE). [TPA is a phorbol ester, ~ecanoyl phorbol acetate, which is a chemical tumor promoter] ...

See also: See also: What is the meaning of Cell, Chromosome, Cells, Protein, Animal?

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