Chiasmata
During the first meiotic division, homologous chromosomes pair up to form bivalents. Each bivalent consists of two pairs of sister chromatids, with one chromatid from each homologous chromosome. The non-sister chromatids of the bivalent come in contact with each other at specific points called chiasmata.

Formation of Bivalents
Before the first meiotic division, DNA replication occurs, resulting in the formation of sister chromatids. Homologous chromosomes then pair up and undergo synapsis, where they align themselves closely together. This alignment allows for the exchange of genetic material between non-sister chromatids.

Homologous Recombination
The exchange of genetic material between non-sister chromatids is known as homologous recombination. It involves the physical breaking and rejoining of DNA strands, leading to the exchange of genetic material between the homologous chromosomes. This process promotes genetic diversity by shuffling genetic information between homologous chromosomes.

Formation of Chiasmata
During homologous recombination, the non-sister chromatids of the bivalent align and exchange genetic material. As a result, cross-like structures called chiasmata are formed. Chiasmata are visible under a microscope and can be observed as points of contact between non-sister chromatids.

Significance of Chiasmata
Chiasmata play a crucial role in ensuring proper segregation of chromosomes during meiosis. They help to hold the homologous chromosomes together, allowing for the proper alignment and separation of chromosomes during the first meiotic division. Chiasmata also contribute to genetic diversity by facilitating the exchange of genetic material between homologous chromosomes.

Conclusion
In summary, cross-like configurations known as chiasmata are formed when non-sister chromatids of a bivalent come in contact during the first meiotic division. Chiasmata are important for proper chromosome segregation and the generation of genetic diversity.