Formation of X-shaped structure during meiosis

Meiosis is a type of cell division that produces gametes with half the number of chromosomes as the parent cell. During meiosis, several distinct stages occur, each with its own specific characteristics. One of the key events during meiosis is the formation of an X-shaped structure, known as a bivalent or tetrad. This structure is formed during the following stage:

1. Zygotene

During the zygotene stage of meiosis, homologous chromosomes begin to pair up and become closely associated. This pairing is facilitated by the formation of protein complexes called synaptonemal complexes, which help align the chromosomes. As the homologous chromosomes come together, they form a structure that resembles an X shape. This X-shaped structure represents the physical connection between the paired homologous chromosomes and is crucial for ensuring proper genetic exchange between them.

In summary, the X-shaped structure is formed during the zygotene stage of meiosis when homologous chromosomes pair up and become closely associated. This structure plays a vital role in promoting genetic recombination and ensuring the proper segregation of chromosomes during meiosis.