How Do Telophase I And Telophase Ii Differ During Meiosis In Animal Cells?
Epitomize: What is Meiosis?
Meiosis is how eukaryotic cells (plants, animals, and fungi) reproduce sexually. It is a process of chromosomal reduction, which ways that a diploid cell (this means a jail cell with two complete and identical chromosome sets) is reduced to form haploid cells (these are cells with merely one chromosome set). The haploid cells produced past meiosis are germ cells, besides known as gametes, sexual activity cells or spores in plants and fungi. These are essential for sexual reproduction: two germ cells combine to form a diploid zygote, which grows to form another functional adult of the aforementioned species.
The process of chromosomal reduction is important in the conservation of the chromosomal number of a species. If chromosome numbers were not reduced, and a diploid germ cell was produced by each parent, and so the resulting offspring would have a tetraploid chromosome set up: that is, it would accept iv identical sets of chromosomes. This number would continue increasing with each generation. This is why the chromosomal reduction is vital for the continuation of each species.
Meiosis occurs in two distinct phases: meiosis I and meiosis Ii. There are many similarities and differences between these phases, with each phase producing different products and each stage being equally crucial to the production of feasible germ cells.
What Happens Earlier Meiosis?
Before meiosis, the chromosomes in the nucleus of the prison cell replicate to produce double the amount of chromosomal material. After chromosomal replication, chromosomes separate into sister chromatids. This is known as interphase, and can exist further broken down into ii phases in the meiotic cycle: Growth (G), and Synthesis (South). During the G stage proteins and enzymes necessary for growth are synthesized, while during the S phase chromosomal material is doubled.
Meiosis is then split into 2 phases: meiosis I and meiosis Two. In each of these phases, in that location is a prophase, a metaphase, and anaphase and a telophase. In meiosis I these are known every bit prophase I, metaphase I, anaphase I and telophase I, while in meiosis II they are known as prophase II, metaphase Ii, anaphase II and telophase II. Different products are formed by these phases, although the basic principles of each are the aforementioned. Also, meiosis I is preceded in interphase by both K phase and S phase, while meiosis Ii is just preceded by Due south phase: chromosomal replication is not necessary once again.
The Phases of Meiosis I
Afterward Interphase I meiosis I occurs after Interphase I, where proteins are grown in Chiliad stage and chromosomes are replicated in South phase. Following this, four phases occur. Meiosis I is known every bit reductive division, every bit the cells are reduced from being diploid cells to existence haploid cells.
1. Prophase I
Prophase I is the longest phase of meiosis, with three main events occurring. The first is the condensation of chromatin into chromosomes that tin be seen through the microscope; the 2d is the synapsis or concrete contact betwixt homologous chromosomes; and the crossing over of genetic material between these synapsed chromosomes. These events occur in 5 sub-phases:
- Leptonema– The start prophase event occurs: chromatin condenses to form visible chromosomes. Condensation and coiling of chromosomes occur.
- Zygonema– Chromosomes line upwards to form homologous pairs, in a procedure known as the homology search. These pairs are likewise known as bivalents. Synapsis happens when the homologous pairs join. The synaptonemal complex forms.
- Pachynema– The third main event of prophase I occurs: crossing over. Nonsister chromatids of homologous chromosome pairs exchange parts or segments. Chiasmata form where these exchanges have occurred. Each chromosome is at present different to its parent chromosome merely contains the same amount of genetic textile.
- Diplonema– The synaptonemal circuitous dissolves and chromosome pairs begin to separate. The chromosomes uncoil slightly to allow Dna transcription.
- Diakinesis – Chromosome condensation is furthered. Homologous chromosomes split further but are even so joined by a chiasmata, which moves towards the ends of the chromatids in a process referred to every bit terminalization. The nuclear envelope and nucleoli disintegrate, and the meiotic spindle begins to form. Microtubules attach to the chromosomes at the kinetochore of each sis chromatid.
2. Metaphase I
Homologous pairs of chromosomes align on the equatorial plane at the center of the cell. Independent assortment determines the orientation of each bivalent but ensures that half of each chromosome pair is oriented to each pole. This is to ensure that homologous chromosomes practise not end up in the same cell. The arms of the sister chromatids are convergent.
three. Anaphase I
Microtubules begin to shorten, pulling ane chromosome of each homologous pair to opposite poles in a procedure known every bit disjunction. The sister chromatids of each chromosome stay connected. The prison cell begins to elongate in grooming for cytokinesis.
4. Telophase I
Meiosis I ends when the chromosomes of each homologous pair arrive at opposing poles of the cell. The microtubules atomize, and a new nuclear membrane forms effectually each haploid set of chromosomes. The chromosomes uncoil, forming chromatin again, and cytokinesis occurs, forming two non-identical daughter cells. A resting phase known equally interkinesis or interphase II happens in some organisms.
The Phases of Meiosis 2
Meiosis II may begin with interkinesis or interphase II. This differs from interphase I in that no S stage occurs, every bit the Dna has already been replicated. Thus only a Grand phase occurs. Meiosis II is known as equational sectionalization, as the cells begin as haploid cells and cease as haploid cells. There are once again four phases in meiosis II: these differ slightly from those in meiosis I.
1. Prophase II
Chromatin condenses to course visible chromosomes once more. The nuclear envelope and nucleolus disintegrate, and spindle fibers begin to appear. No crossing over occurs.
2. Metaphase 2
Spindle fibers connect to the kinetochore of each sister chromatid. The chromosomes marshal at the equatorial plane, which is rotated 90° compared to the equatorial plane in meiosis I. Ane sister chromatid faces each pole, with the arms divergent.
3. Anaphase Two
The spindle fibers connected to each sister chromatid shorten, pulling ane sis chromatid to each pole. Sis chromatids are known as sister chromosomes from this signal.
4. Telophase II
Meiosis Ii ends when the sister chromosomes have reached opposing poles. The spindle disintegrates, and the chromosomes recoil, forming chromatin. A nuclear envelope forms effectually each haploid chromosome fix, before cytokinesis occurs, forming two daughter cells from each parent cell, or four haploid daughter cells in full.
Figure 1. The phases of meiosis I and meiosis II, showing the formation of four haploid cells from a single diploid cell.
How is Meiosis I Different from Meiosis II?
Meiosis is the product of four genetically diverse haploid daughter cells from ane diploid parent cell. Meiosis tin but occur in eukaryotic organisms. Information technology is preceded past interphase, specifically the G phase of interphase. Both Meiosis I and 2 take the same number and arrangement of phases: prophase, metaphase, anaphase, and telophase. Both produce two girl cells from each parent jail cell.
However, Meiosis I begins with one diploid parent jail cell and ends with two haploid daughter cells, halving the number of chromosomes in each cell. Meiosis II starts with two haploid parent cells and ends with four haploid daughter cells, maintaining the number of chromosomes in each prison cell. Homologous pairs of cells are nowadays in meiosis I and separate into chromosomes before meiosis Two. In meiosis II, these chromosomes are further separated into sister chromatids. Meiosis I includes crossing over or recombination of genetic material between chromosome pairs, while meiosis II does non. This occurs in meiosis I in a long and complicated prophase I, carve up into five sub-phases. The equatorial aeroplane in meiosis 2 is rotated 90° from the alignment of the equatorial aeroplane in meiosis I.
The tabular array below summarizes the similarities and differences between meiosis I and meiosis II.
Tabular array 1. The similarities and differences between meiosis I and meiosis II.
| Meiosis I | Meiosis 2 |
Similarities | |
| Can only occur in eukaryotes | |
| G phase of interphase usually occurs first | |
| Product of daughter cells based on parent cell's genetic cloth | |
| Means of sexual reproduction in plants, animals, and fungi | |
| 4 phases occur: prophase, metaphase, anaphase, telophase | |
Differences | |
| Starts as diploid; ends as haploid | Starts as haploid; ends as haploid |
| Reductive division | Equational division |
| Homologous chromosome pairs separate | Sister chromatids separate |
| Crossing over happens | Crossing over does not happen |
| Complicated sectionalization process | Simple division process |
| Long duration | Short elapsing |
| Preceded by S-phase and G-phase | Preceded merely by Yard-phase |
| Sis chromatids in prophase have convergent arms | Sis chromatids in prophase accept divergent arms |
| Equatorial plane is centered | Equatorial plane is rotated 90° |
| Prophase separate into five sub-phases | Prophase does not accept sub-phases |
| Ends with ii daughter cells | Ends with 4 daughter cells |
Why is Meiosis Important?
Meiosis is essential for the sexual reproduction of eukaryotic organisms, the enabling of genetic diverseness through recombination, and the repair of genetic defects.
The crossing over or recombination of genes occurring in prophase I of meiosis I is vital to the genetic diversity of a species. This provides a buffer confronting genetic defects, susceptibility to illness and survival of possible extinction events, as there will always exist sure individuals in a population improve able to survive changes in environmental status. Recombination further allows genetic defects to exist masked or even replaced by healthy alleles in offspring of diseased parents.
Meiosis I and Meiosis II Biology Review
We now know that meiosis is the process of the production of haploid daughter cells from diploid parent cells, using chromosomal reduction. These daughter cells are genetically distinct from their parent cells due to the genetic recombination which occurs in meiosis I. This recombination is essential for genetic diversity within the population and the correction of genetic defects.
Meiosis I and II are similar in some aspects, including the number and organisation of their phases and the production of ii cells from a unmarried cell. Withal, they also differ greatly, with meiosis I being reductive sectionalisation and meiosis II existence equational division. In this manner, meiosis Ii is more than similar to mitosis. Both stages of meiosis are of import for the successful sexual reproduction of eukaryotic organisms.
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