tetrad


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Related to tetrad: Tetrad analysis

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 ?
Additionally, the correlation between the calculated values of the tetrad effect with aforementioned geochemical factors will be also discussed.
Neil Stephenson and Kelly Adamson, Tetrad Recruitment Group
The structure coefficients [C.sup.c.sub.ab] appear in commutation relation of the tetrad as
People involved in a company's human resources office, for example, know that those with the Dark Tetrad of conditions can be quite good at getting through job interviews and even screening tests, and then become a real pain once they start working.
Such examples suggest a fascinating series of analogies within the tetrad: reversal (4), for example, can be thought of as an obsolescence (2) of the intensification (1), and/or a retrieval (3) of the obsolesced (2).
Tetrad thymines had been replaced by the synthetic 5-bromouracil ([br.sup.5]U) and 5-aminouracil (n U) (Figure 4, 7, 8) that substituted for the central T of TGGTGGT.
It is interesting to think about the tetrad in the context of digital media and their implications for the management of R&D (Table 2).
May 4 ~ May 7###Microspore tetrad stage###Inner and outer integument initiation to elongation
The tetrad is an analytical model created by McLuhan to facilitate the translation of user experiences of media.
Many believe this eclipse was significant as it marks the completion of an unusual line-up of four total eclipses at six-monthly intervals known as a "tetrad".
It will also mark the completion of a "biblical tetrad" - a rare sequence of four total lunar eclipses occurring at six-monthly intervals.