Diplotene Stage: Description & Importance | Meiosis
Diplotene is the fourth subphase of prophase I of meiotic cell division and is distinguished by the separation of chromatids from homologous chromosomes. During this subphase, you can see the places on the chromosomes where recombination occurred, those places are called chiasms.
A recombination occurs when a strand of genetic material is cut to bind to another molecule with different genetic material. During diplotene, Meiosis can experience a state of pause or latency experienced by the eggs, which is called acetylene.
In this case, the human ovules will cease their activity, until the seventh month of embryonic development and, the activity will restart, at the moment the individual reaches sexual maturity.
Diplotene starts when the chromosomes separate and simultaneously increase in size and separate from the nuclear membrane. Tetrads (two chromosomes) of four chromatids are formed and the sister chromatids in each tetrad are joined by the centromeres. The chromatids that have crossed will be united by chiasms.
Meiosis Definition
Meiosis is a specialized class of cell division that cuts the number of chromosomes in half, producing four haploid cells.
Each haploid cell is genetically different from the stem cell that originated it and comes from the sex cells, also called gametes
This procedure happens in all unicellular (eukaryotic) and multicellular beings of sexual reproduction: plants, Animal cells, and fungi. When errors occur in meiosis, aneuploidy is evident and it is the leading known cause of miscarriage and the most common genetic cause of disabilities.
Phases of Meiosis
The meiotic process is carried out in two stages or phases: Meiosis I and Meiosis II.
Meiosis I, in turn, consists of four stages: prophase I, metaphase I, anaphase I, and telophase.
The first division is the more specialized of the two divisions: the cells that result from it are haploid. At this stage, there is a reductional division of the genome and its most important moment is prophase, which is a long and complex stage in which the separation of homologous chromosomes occurs.
In prophase I, homologous chromosomes are paired and there is an exchange of DNA (homologous recombination). Chromosomal crossing occurs, which is a decisive process for the coupling of homologous chromosomes and, consequently, for the specific separation of chromosomes in the first division.
Read: DNA Replication
The new DNA mixtures produced at the crossing are a significant source of genetic variation that results in new allele combinations, which can be very favorable for the species. The paired and replicated chromosomes are called bivalent or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. The coupling of homologous chromosomes is called a synapse. At this stage, non-sister chromatids can cross at points called chiasms (plural; singular chiasma).
Prophase I is the longest phase of meiosis. It is divided into five substages that are named based on the appearance of the chromosomes: leptotene, zygotene, pachytene, diplotene, and diakinesis.
Before the diplotene sub-stage begins, homologous recombination occurs, and crosses occur between the chromosomes of the non-sister chromatids, in their chiasms. At that precise moment, the chromosomes remain tightly paired.
What is Diplotene?
Diplotene, also called diplonema, (from the Greek Diplo: double and taenia: tape or thread) is the sub-stage that happens before pachytene. Before diplotene, homologous chromosomes have paired into tetrads or bivalents (genetic value of both parents), shorten, thicken, and sister chromatids differentiate.
A zipper-like structure, called the synaptonemal complex, forms between chromosomes that have paired and then degrade, at the diplotene stage, causing the homologous chromosomes to separate slightly.
The chromosomes unwind, allowing DNA transcription. However, the homologous chromosomes from each pair formed remain tightly bound in the chiasms, the regions where the crossing occurred. The chiasms remain on the chromosomes until they separate at the transition to anaphase I.
In diplotene, the synaptonemal complexes separate, the central space enlarges and the components disappear, remaining only in the regions where there were chiasms. The lateral elements are also kept present, which are fine and separate from each other.
In advanced diplotene the axes are interrupted and disappear, only remnants remain in the centromeric and chiasmatic regions.
Upon recombination, the synaptonemal complex disappears and the members of each bivalent pair begin to separate. In the end, the two homologs of each bivalent only remain linked at the cross-points (chiasms).
The average number of chiasms in human spermatocytes is 5, that is, several per bivalent. In contrast, the proportion of oocytes in pachytene and diplotene increases in fetal development.
As they get closer to diplotene, the oocytes enter the so-called meiotic or dichytotene arrest. At approximately six months of gestation, all the germ cells will be in this substage.
Importance of the diplotene substage
Around the eighth month of embryonic development, the oocytes are more or less synchronized in the diplotene stage of prophase I.
The cells will remain in this subphase from birth until puberty, when the ovarian follicles begin to mature one by one and the oocyte restarts the final phase of diplotene.
During the process of oogenesis (creation of the ovules), human oocytes stop their maturation process at the diplotene stage, before birth. Upon reaching the puberty phase, the process is restarted, this suspended state of the meiotic division is known as dictyotene or dictyate.
When ovulation begins, the oocyte is between the first and second meiotic divisions. The second division is suspended until fertilization, which is when the anaphase of the second division occurs and the female pronucleus is ready to unite with the male.
This resumption of oocyte maturation occurs to prepare them for ovulation.
Frequently Asked Questions on Diplotene
What is the diplotene phase?
Answer: Definition of diploma. : A phase of meiotic prophase that follows the pachytene and during which the paired homologous chromosomes begin to separate and become visible.
What happens in diplotene?
Answer: Diplotene. The first phase of the meiotic prophase follows the pachytene, in which two chromosomes in each binomial begin to repel each other and there is a division between the chromosomes.
What is the evolutionary significance of the diplotene phase?
Answer: The developmental importance of the diplomatic state is that at this stage there is a crossing of genes from 2 different cells or chromosomes, which helps in the formation of a single zygote from 2 different gametes.
How is Chismata formed?
Answer: The physical link, which is the point of contact, is related to homologous chromosomes between two (non-sister) chromatids. During the diplomatic phase of prophase I of meiosis, pores appear, but the actual “crossing-over” of the genetic material is considered during the last twenty-five phases.
When can Chiasmata be seen for the first time?
Answer: During the diplomatic phase of prophase I of meiosis, pores appear, but the actual “crossing-over” of the genetic material is considered during the last twenty-five phases.