Bivalent (genetics)

A bivalent or a tetrad is a structure of chromosomes during maturation (meiosis ) is formed from germ cells of the eukaryotes. In this structure, which occurs in pachytene of meiosis, the chromosomes are already duplicated so that each chromosome consists of two chromatids. In addition, the homologous chromosomes, ie the maternal and paternal copies of a chromosome, closely paired. In this stage, the recombination by crossing-over occurs. The term tetrad derived from the four distinguishable chromatids, chromosomes, the term bivalent of the two involved.

Unpaired chromosomes that occur before or after mating, are sometimes referred to as univalents.

The four germ cells which arise at meiosis, can be referred to as a nibble.

Swell

• Frederick W. Stöcker, Gerhard Dietrich (ed.): Brockhaus ABC biology. Volume 1: A - Me 6, revised and expanded edition. FA Brockhaus Verlag, Leipzig, 1986, ISBN 3-325-00073-8.
• CE M'Clung: The Spermatocyte Divisions of the Acrididae. In: Kansas University Quarterly. Series A: Science and Mathematics. Vol 9, 1900, ISSN 0885-4068, pp. 73-100, here p 78, The term " chromosome " being [ ... ] restricted to the units of the division figures, there remains no name for the parts composing synthesis whenthey are compound, as in tetrads and diads [ ... ] I like shoulderstand, THEREFORE, to propose the term " chromatid " for each of the synthesis [ ... ]. Digitized.
• J. Howard McGregor: The Spermatogenesis of Amphiuma. In: Journal of Morphology. Vol 15, Supplement, 1899, ISSN 0898-9249, pp. 57-104, here p 81, [ ... ] and the only Possibility of a true reduction [ ... ] is by conceiving the chromosomes to be " bivalent " [ ... ] and to assume [ ... ] did the halves of synthesis bivalent chromosomes form new connections before the final mitosis. Digitized.

• Genetics
• Chromosome