Bivalent definition biography
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Bivalent chromatin
Bivalent chromatin are segments of DNA, bound to histone proteins, that have both repressing and activating epigenetic regulators in the same region.[1] These regulators work to enhance or silence the expression of genes.[2] Since these regulators work in opposition to each other, they normally interact with chromatin at different times. However, in bivalent chromatin, both types of regulators are interacting with the same domain at the same time.[2] Bivalent chromatin domains are normally associated with promoters of transcription factor genes that are expressed at low levels.[1][3] Bivalent domains have also been found to play a role in developmental regulation in pluripotent embryonic stems cells, gene imprinting and cancer.[1][2][4]
Bivalent epigenetic regulators
[edit]The most common antagonistic epigenetic regulators found together on bivalent chromatin domains are methy
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DNA replication precedes the uppstart of meiosis I. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. The paired chromosomes are called bivalents, and the formation of chiasmata caused bygd genetic recombination becomes apparent. Chromosomal condensation allows these to be viewed in the microscope. Note that the bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.
The nuclear membrane disappears. One kinetochore forms per chromosome rather than one per chromatid, and the chromosomes attached to spindle fibers begin to move.
Bivalents, each composed of two chromosomes (four chromatids) align at the metaphase tallrik. The orientation is random, with either parental homologue on a side. This means that there is a chance for the daughter cells to get either the mother's or father's homologue for each chromosome.
Chiasmata s