Meiosis I

Meiosis I, also known as reductional division, is the first cell division of meiosis that produces two haploid cells from a diploid cell. Meiosis I is divided into four distinct stages – prophase I, metaphase I, anaphase I, and telophase I.

Prophase I consists of five substages – leptotene, zygotene, pachytene, diplotene, and diakinesis.

In leptotene, the chromosomes begin to condense, appearing as a thread-like, beaded structure where each chromosome consists of a pair of sister chromatids held together by  cohesin complexes.

At the onset of zygotene, homologous chromosomes pair to form tetrads.

The pairing, also known as synapsis, occurs lengthwise where each gene segment of paternal chromosomes pairs with its counterpart on the maternal chromosome. 

A protein based ladder-like structure called the synaptonemal complex forms between the paired chromatids.  This complex aids pairing and recombination of the chromosomes.

In pachytene, the exchange of equal chromosome segments or crossing over occurs between two homologous chromosomes. The chromosomes connect at the point of the crossover called chiasma.

During diplotene, the synaptonemal complex breaks down and the paired chromosom