Explanation

Bivalent A pair of homologous chromosomes lying together is called a bivalent. (i) Tetrad In pachytene stage, the chromatids of each synapsed chromosome slightly separate and become visible. The two visible chromatids of a chromosome are referred to as dyad (ii) A group of four homologous chromatids (two dyads) is called a tetrad (iii) Pachytene Stage Crossing over occurs during pachytene stage (iv) Non-sister Chromatids The two chromatids of two homologous chromosomes (bivalent) are termed non-sister chromatids (v) Sister Chromatids The two chromatids of the same chromosome are called sister chromatids