Difference Between Pachytene and Diplotene

The key difference between pachytene and diplotene is that pachytene is the third substage of prophase I during which crossing over and DNA exchange between nonsister chromatids take place while diplotene is the fourth substage of prophase I during which synapsis ends, and charismata become visible within bivalents.

Meiosis is one of the two types of cell division. It produces four daughter cells that contain half of the genetic material (n) possessed by the parental cell. Meiotic cell division takes place during sexual reproduction to produce gametes. The parent cell divides twice to produce four daughter cells. These two-step divisions are known as meiosis I and meiosis II. Each round of division is again divided into sub-stages as prophase, metaphase, anaphase, and telophase. Prophase I is the longest and most important phase of meiosis I.

During prophase I, maternal and paternal homologous chromosomes pair with each other, cross over and exchange their genetic materials in order to produce genetically different gametes. Prophase I has five sub-phases named according to the appearance of the chromosomes. These subphases are leptotene, zygotene, pachytene, diplotene, and diakinesis. In pachytene, synapsis is completed while in diplotene, chiasmata are evident.

CONTENTS

1. Overview and Key Difference
2. What is Pachytene 
3. What is Diplotene
4. Similarities Between Pachytene and Diplotene
5. Side by Side Comparison – Pachytene vs Diplotene in Tabular Form
6. Summary

What is Pachytene?

Pachytene is the third sub-stage of prophase 1 of meiosis 1. During pachytene, the synaptonemal complex is complete, allowing chiasma to form. Then the crossing over takes place between nonsister chromatids; this forms bivalents.

Moreover, in fully zipped up tetrads, the exchange of genetic material between mother and father takes place, introducing new genetic compositions to gametes. Thus, this phase is very crucial since it is responsible for the genetic variation between organisms.

What is Diplotene?

Diplotene is the fourth substage of prophase I. It occurs after pachytene and is followed by diakinesis. During diplotene, synapsis ends, so synaptonemal complexes disappear. Chromosomes condense further.

Chiasmata become fully visible within bivalents under the microscope. Homologous chromosome pairs begin to migrate apart but remain attached at chiasmata.

What are the Similarities Between Pachytene and Diplotene?

• Pachytene and diplotene are two substages of prophase I of meiosis I.
• Both phases are responsible for the genetic variation between organisms.
• In both phases, homologous chromosomes remain closed to each other.

What is the Difference Between Pachytene and Diplotene?

Pachytene is that third substage of prophase I during which crossing over and genetic recombination take place. Diplotene is the fourth substage of prophase I during which homologous chromosomes begin to move apart, chiasmata become visible, and synaptonemal complex disappears. So, this is the key difference between pachytene and diplotene. Besides, pachytene is followed by diplotene while diplotene is followed by diakinesis. Moreover, synapsis is completed by pachytene while synapsis ends in diplotene. Thus, this is another difference between pachytene and diplotene.

The below info-graphic shows the differences between pachytene and diplotene in tabular form.

Summary – Pachytene vs Diplotene

Pachytene and diplotene are two substages of prophase I of meiosis I. During pachytene, the synaptonemal complex is complete, allowing bivalents to form. Therefore, crossing over takes place between nonsister chromatids, facilitating the genetic recombination between mother and father genetic material. Pachytene is followed by diplotene. During diplotene, homologous chromosomes begin to move apart. But they remain attached at chiasmata. Therefore, the synaptonemal complex dissociates, and chiasmata become visible in this stage. Thus, this summarizes the difference between pachytene and diplotene.

Reference:

1. “Prophase.” Wikipedia, Wikimedia Foundation, 22 Jan. 2021, Available here.
2. “Pachytene.” Pachytene – an Overview | ScienceDirect Topics, Available here.

Image Courtesy:

1. “Meiosis Prophase I” By Huanyu Qiao, Jefferson K. Chen, April Reynolds, Christer Höög, Michael Paddy, Neil Hunter – Figure 1 from "Interplay between Synaptonemal Complex, Homologous Recombination, and Centromeres during Mammalian Meiosis" PLOS Genetics https://doi.org/10.1371/journal.pgen.1002790.g001 (CC BY 4.0) via Commons Wikimedia
2. “Synaptonemal Complex” By Daniel Wells – Delineation of meiotic gene expression in male mice (2020) PhD Thesis (CC BY-SA 4.0) via Commons Wikimedia