quiasma

A chiasma, plural chiasmata, is the point of contact between homologous chromosomes during meiosis. This crucial crossover event occurs during prophase I of meiosis, specifically in the pachytene stage. At a chiasma, the synaptonemal complex, a protein structure that holds homologous chromosomes together, begins to disassemble. This disassembly allows for the physical exchange of genetic material between non-sister chromatids of the homologous chromosomes.

The formation of chiasmata is essential for proper chromosome segregation during meiosis. The chiasmata serve as physical links that hold the homologous chromosomes together until anaphase I. Without these connections, homologous chromosomes might separate prematurely, leading to aneuploidy in the resulting gametes. The number and position of chiasmata can vary between different chromosome pairs and even between individuals. They play a significant role in genetic recombination, introducing new combinations of alleles into the offspring and contributing to genetic diversity within a population. The study of chiasmata is important in understanding the mechanisms of inheritance and chromosomal abnormalities.