Crossing Over

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•  The early stages of meiosis involve pairing of homologous chromosomes and crossing over 

    followed by condensation

In prophase I, homologous chromosomes undergo a process called synapsis, whereby they pair up to form a bivalent (or tetrad)

  • The homologous chromosomes are held together at points called chiasmata (singular: chiasma)

Crossing over of genetic material between non-sister chromatids can occur at these chiasmata

  • As a result of this exchange of genetic material, new gene combinations are formed on chromatids (recombination)

Once chiasmata are formed, the homologous chromosomes condense as bivalents and then are separated in meiosis

  • If crossing over occurs then all four haploid daughter cells will be genetically distinct (sister chromatids are no longer identical)

Crossing Over

Crossing over