tetrad

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Related to Tetrads: meiosis

tetrad

1. a group or series of four
2. the number four
3. Botany a group of four cells formed by meiosis from one diploid cell
4. Genetics a four-stranded structure, formed during the pachytene stage of meiosis, consisting of paired homologous chromosomes that have each divided into two chromatids
5. Chem an element, atom, group, or ion with a valency of four
6. Ecology a square of 2 × 2 km used in distribution mapping

Tetrad

 

(1) A group of four haploid cells formed by meiosis from a single diploid cell. Tetrads are typical of plants. In mosses, fungi, and algae, such four-celled groups may remain for a long time within the membrane of the parent cell. By isolating the cells of the tetrad in these organisms, vegetative offspring may be obtained and the genetic division in each meiosis may be studied by means of tetrad analysis. Ordered arrangements of cells may occur in tetrads; the chromosome groups in the cells of such tetrads reflect the order in which the chromosomes of two successive meioses separate. These cells, called linear asci, are typical of some ascomycete fungi.

(2) In tetrad analysis, the four cultures obtained by the vegetative propagation of spores formed after the meiosis of a single diploid cell.

(3) A structure composed of four connected chromatids. It is observed in animal cells during the prophase of the first, or reductive, division of meiosis. Such tetrads are also called bivalents.

I. I. TOLSTORUKOV

tetrad

[′te‚trad]
(cell and molecular biology)
A group of four chromatids lying parallel to each other as a result of the longitudinal division of each of a pair of homologous chromosomes during the pachytene and later stages of the prophase of meiosis.
References in periodicals archive ?
10 Sarcina bacteria can be differentiated from Staphylococcus species, even though both organisms are gram positive, because Staphylococcus bacteria, at approximately 1 [micro]m in diameter, is much smaller and is arranged in characteristic grapelike clusters, rather than a tetrad pattern.
The microspores soon separated from each other and were released from the tetrads as free microspores (Figs.
The Use of tetrads in the analysis of arts-based media.
In 1493, a tetrad saw the expulsion of Jews by the Catholic Spanish Inquisition.
It's not just evangelical Christians, messianic Jews and Hebrew roots believers touting something big, something significant in the tetrad of blood moons set for a grand finale "supermoon" show on September 28.
These incredible pictures captured the drama of the blood moon eclipse - the first of a series known as a tetrad.
Farming improvements of old pasture land in the 1950s and '60s reduced the availability of ants and resulted in loss from one-third of the tetrads occupied since 1970.
Because of pancytopenia (Table), a bone marrow biopsy was performed and showed intraerythrocytic ring forms with tetrads.
After this initial period, monads, dyads and tetrads without envelopes appeared and were followed by free hilate monads and trilete spores.
1) When there are many tetrads there are also many ITLEs.
In the chromosomes segregation process, the observed irregularities were: precocious chromosomes migration in metaphases (Figure 1C and I), laggard chromosomes in anaphases (Figure 1D and J), micronuclei in telophases (Figure 1F, K and L), and tetrads with microcytes (Figure 2D).