Answer:
A tetrad is a four part structure formed during the prophase I of meiosis I which is formed by the homologous chromosomes which is composed of two identical chromatids.
The tetrad formation takes place when a proteinaceous meiosis-specific nuclear structures called synaptonemal complex is formed between two homologous chromosomes which mediates the tight associations of the homologous chromosomes.
The synaptonemal complex consists of two ladder like lateral elements which attaches the chromatin of the homologius chromosomes. The central region of the synaptonemal complex is composed of the transverse filaments and the central element which bridge the space between the the lateral elements.
This attachment of the chromatin to the synaptonemal complex mediates the chromosome pairing and form tetrad.
D