Describe various subphases of prophase - $I$ of Meiosis - $I$.

(N/A) $ \Rightarrow $ Prophase - $I$ of Meiosis - $I$: It is longer and more complex. It has been subdivided into five subphases based on chromosomal behavior.
$(i)$ Leptotene: This is the first phase of meiosis. During this phase,the chromosomes become gradually visible. The compaction of chromosomes continues throughout Leptotene.
$ \Rightarrow $ Each chromosome is made up of two chromatids and a centromere attached to them. However,the chromatids are tangled with each other,so their dual form is not clearly seen.
$(ii)$ Zygotene: During this stage,chromosomes start pairing together,and this process of association is called synapsis. Such paired chromosomes are called homologous chromosomes.
$ \Rightarrow $ This process proceeds further like a zipper. The complex formed by a pair of synapsed homologous chromosomes is called a bivalent or a tetrad.
$(iii)$ Pachytene: During this stage,bivalent chromosomes clearly appear as tetrads. The non-sister chromatids of the homologous chromosomes are entangled with each other.
$ \Rightarrow $ This stage is characterized by the appearance of recombination nodules.
$ \Rightarrow $ Crossing over occurs between non-sister chromatids of the homologous chromosomes.
$ \Rightarrow $ Crossing over is the exchange of genetic material between two homologous chromosomes,which is an enzyme-mediated process involving the enzyme recombinase.
$ \Rightarrow $ Crossing over leads to the recombination of genetic material on the two chromosomes,forming new combinations.
$(iv)$ Diplotene: The beginning of diplotene is recognized by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other,except at the sites of crossing over.
$ \Rightarrow $ These $X$-shaped structures are called chiasmata.
$ \Rightarrow $ The number of chiasmata depends on the length of the chromosomes.
$(v)$ Diakinesis: This is the final stage of meiotic prophase - $I$. The chiasmata terminate. The nucleolus disappears and the nuclear envelope breaks down. The chromosomes are fully condensed and the meiotic spindle is assembled to prepare the homologous chromosomes for separation.