Chiasmata is the X-shaped structure formed due to the point of contact between paired chromatids during meiosis. It is the point representing the crossover where the homologous chromosomes are joined to each other.
Significance: At chiasmata crossing over occurs in the pachytene stage. The genetic constitution of the daughter cells differs from the parent cells due to crossing over. There is a mixture of the paternal and maternal gene in each chromosome of daughter cells mostly.