Bivalent (genetics)

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A bivalent is sometimes referred to as a tetrad.

During mitosis, bivalents are a pair of associated homologous chromosomes formed after replication. Each replicated chromosome comprises of two chromatids.

During meiosis, bivalents are made up of a pair of homologous dyads. A dyad is a pair of sister chromatids with an undivided centromere. A dyad is formed after DNA replication in Prophase I of meiosis. So a bivalent contains a total of four chromatids. The homologous dyads pair with one another during Metaphase I of meiosis. The homologous dyads are separated when these bivalents are pulled apart by spindle fibers during Anaphase I of meiosis.

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