Final answer:
During prophase I of meiosis, homologous chromosomes form a tetrad and chiasmata form between non-sister chromatids. Crossing over occurs at the chiasmata, promoting genetic diversity. Chiasmata play a crucial role in chromosome segregation during meiosis.
Step-by-step explanation:
During prophase I of meiosis, homologous chromosomes pair up and form a structure called a tetrad. The tetrad consists of two homologous chromosomes, each made up of two sister chromatids. Chiasmata, which are points of contact between non-sister chromatids, then form between the homologous chromosomes. Crossing over occurs at the chiasmata, where genetic material is exchanged between the non-sister chromatids. This process is called homologous recombination (HR) and it promotes genetic diversity by creating new combinations of genes on each chromosome.
Chiasmata play a role in chromosome segregation during meiosis. They hold the paired homologous chromosomes together and ensure that they separate correctly during the subsequent meiotic divisions. The number of chiasmata varies, but there must be at least one chiasma per chromosome to ensure proper homologous chromosome separation.