Pachytene is the third stage of meiosis prophase-1 (a five-stage process). It is preceded by the zygotene stage, where synapsis, i.e. pairing of homologous chromosomes take place.
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In the pachytene stage, the tetrad formed due to synapsis become distinct and four chromatids become clearly visible. There are four kinetochores present in each tetrad
Recombination or crossing over takes place at this stage. In this process, there is an exchange of genetic material between non-sister chromatids of homologous chromosomes. There is rearrangement and reshuffling of the genetic material of two parental homologous chromosomes. It is an enzyme-mediated process. The enzyme involved in crossing over is known as recombinase.
Recombination nodules appear and homologous chromosomes are linked to each other at the site of crossing over.
Recombination is accompanied by the formation of chiasmata, which appear in the next stage called diplotene.
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