Meiotic arrest at diplotene stage commonly occurs in mammalian occytes. In females, meiosis starts in the embryo and proceeds as for as diplotene, when the chromosomes become diffused and the cells are referred to as being in the dictuate stage. This arrest is under hormonal control.
In many amphibian oocytes binds and insects with a long period of immaturity, the oocyte may be arrested in the dictyate stage for many years and spend a prolonged period in diplotene.
This stage is characterised by formation of lampbrush chromosomes where intense RNA synthesis occurs and most of the genes in the DNA loops are actively transcribed and expressed.
Difference between cytokinesis in plant cell and animal cell is as follows
| Cytokinesis in Plant Cell | Cytokinesis in Animal Cell |
|---|---|
| The division of cytoplasm takes place by cell plate formation. | The division of cytoplasm takes place by cleavage. |
| The cell plate formation starts at the centre of the cell and grow outward, toward the lateral walls. | Cleavage starts at the periphery and then moves inward, dividing the cell into two parts. |
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The following contrasting differences reveals that telophase is reverse of prophase, in cell division
| Prophase | Telophase |
|---|---|
| I'st stage of (karyokinesis ) in cell division, Viscosity of cytoplasm increases. The indistinct and interind DNA condense to form elongated chromosomes. The chromatin disappears and chromosome fibres get shortened and thickened. Spindle fibres appears (awards the poles from the centriole connected in animals with astral rays and in plants without asters Nucleolus degenerate completely. Cell organelles such as ER, Golgi complex disorganise, and difference between cytoplasm and nucleoplasm disappears.  |
Last stage of karyokinesis in cell diveision. Viscodity of cytoplasm deereses. Chromosome groups reorganise themselves into nuclei. Chromosomes elongate and overlap each other to form chromatin. Spindle fibres disappear around the poles. Astral rays also disappear in plants. Nuclear envelope appears and two daughter nuclei are formed at the poles. Cell organelles, i.e., ER and Golgi complex are reformed in the cell. Nucleoplasm also appears in the chromatin area. Making it distinct from rest of cytoplasmic area.  |
Prophase-I occurs over a long duration and involves several complicated changes in meiotic cell division. It is important because genetic recombination and variation in sexually reproducing organism occurs due to the events of this phase.
Leptotene
(i) The chromatin network opens out and threads become clear.
(ii) The chromosomes are thin, slender and long.
(iii) Chromosome number is diploid.
Zygotene
(i) Corresponding chromosomes become intimately associated.
(ii) The process of pairing is known as synapse. It is so exact that pairing is not merely between corresponding chromosomes but between corresponding individual units.
(iii) The chromosomes become shorter and thicker.
Pachytene or Pachynema
(i) The synaptic chromosomes become very intimately associated.
(ii) The pair of chromosomes becomes short and thick.
(iii) Crossing over occurs at this stage. Chiasmata are clearly seen.
Diplotene
(i) Homologous chromosomes start separating from one another.
(ii) Chiasmata tend to slip out of the chromosomes. This is known as terminalisation of chiasmata.
(iii) Chromosomes start separating out but the separation is not complete.
(iv) Nuclear membrane and nucleolus start disappearing.
Diakinesis
(i) The bivalents condense further and get randomly distributed.
(ii) The separation of paired chromosomes is almost complete.
(iii) Terminalisation of chiasmata is almost complete.
(iv) Nuclear membrane and nucleolus disappear.
Mitotic cell division results into the increase in the number of cells that have same genetic composition whereas meiosis has its importance in the life cycle of sexually reproducing organisms.
| Mitosis | Meiosis |
|---|---|
| Event Prophase $\bullet$ Chromomeres are not conspicuous. $\bullet$ Prophase is of shorter duration. $\bullet$ Prophase is simpler and is hardly distinguishable into substages. $\bullet$ Each chromosome has two distinct chromatids. $\bullet$ No bouquet stage is recorded. $\bullet$ Chiasmata are absent. |
$\bullet$ Chromomeres are quite conspicuous. $\bullet$ Prophase-I is of longer duration while prophase-II is very brief. $\bullet$ Prophase-I is complicated and is divisible into five substages. Prophase-II is, however, very simple. $\bullet$ Chromosomes of prophase-I do not show distinct chromatids. $\bullet$ Chromosomes of animals and some plants show convergence towards one side during early prophase-l. It is known as bouquet stage. $\bullet$ Chiasmata or visible connections between homologous chromosomes of bivalents are observed during diplotene, diakinesis (prophase-I) and metaphase-I. |
| Metaphase $\bullet$ Centromeres produce a single metaphasic plate. $\bullet$ Chromosomes are independent and do not show connections. $\bullet$ Only the centromeres lie at the equator. The limbs of chromosomes are oriented in various direction. $\bullet$ A centromere is connected with both the spindle poles. $\bullet$ Two chromatids of a chromosome are genetically similar. |
$\bullet$ A double metaphasic plate is formed by centromeres in metaphase-I but only one in metaphase-II. $\bullet$ Homologous chromosomes are interconnected. Hence, the chromosomes occur in pairs or bivalents in metaphase-l. They are however, free in metaphase-II. $\bullet$ Limbs of the chromosomes mostly lie at the equator while the centromeres project towards the poles in metaphase-l. $\bullet$ A centromere is connected to one spindle pole in metaphase-I, but both in metaphase-II. $\bullet$ The two chromatids of a chromosome are often genetically different due to crossing over. |
| Anaphase $\bullet$ A centromere splits length-wise to form two centromeres in the beginning of anaphase. $\bullet$ Anaphasic chromosomes are single stranded. $\bullet$ Similar chromosomes move towards the opposite poles in anaphase. |
$\bullet$ Centromeres do not divide during anaphase-I but do so in anaphase-II. $\bullet$ Chromosomes are double-stranded in anaphase-l, but single stranded in anaphase-II. $\bullet$ Dissimilar chromosomes move toward the opposite poles both in anaphase-l and anaphase-II. |
| Telophase Telophase is longer and produces interphase nuclei. |
$\bullet$ Telophase-l is shorter and nuclei now enter the interphase. |
| Cytokinesis Cytokinesis follows every mitosis. It produces two new cells. |
$\bullet$ Cytokinesis often does not occur after first or reductional division. It is then simultaneous after second division resulting in four new cells. |