What Is The End Result Of Meiosis Ii In Animal Cells?
Recap: What is Meiosis?
Meiosis is how eukaryotic cells (plants, animals, and fungi) reproduce sexually. It is a process of chromosomal reduction, which means that a diploid cell (this ways a cell with two consummate and identical chromosome sets) is reduced to form haploid cells (these are cells with only i chromosome set up). The haploid cells produced by meiosis are germ cells, also known as gametes, sex cells or spores in plants and fungi. These are essential for sexual reproduction: two germ cells combine to grade a diploid zygote, which grows to form another functional adult of the same species.
The procedure of chromosomal reduction is important in the conservation of the chromosomal number of a species. If chromosome numbers were non reduced, and a diploid germ cell was produced past each parent, then the resulting offspring would have a tetraploid chromosome set: that is, information technology would accept four identical sets of chromosomes. This number would go along 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. At that place are many similarities and differences between these phases, with each stage producing different products and each phase existence as crucial to the production of viable germ cells.
What Happens Before Meiosis?
Earlier meiosis, the chromosomes in the nucleus of the cell replicate to produce double the amount of chromosomal material. After chromosomal replication, chromosomes split up into sister chromatids. This is known every bit interphase, and can exist further cleaved downwards into two phases in the meiotic bicycle: Growth (G), and Synthesis (S). During the G stage proteins and enzymes necessary for growth are synthesized, while during the S phase chromosomal material is doubled.
Meiosis is so divide into two phases: meiosis I and meiosis II. In each of these phases, there is a prophase, a metaphase, and anaphase and a telophase. In meiosis I these are known equally prophase I, metaphase I, anaphase I and telophase I, while in meiosis 2 they are known as prophase 2, metaphase 2, anaphase Two and telophase II. Dissimilar products are formed by these phases, although the basic principles of each are the same. Also, meiosis I is preceded in interphase by both 1000 phase and Southward phase, while meiosis Ii is only preceded by S phase: chromosomal replication is non necessary once more.
The Phases of Meiosis I
Subsequently Interphase I meiosis I occurs after Interphase I, where proteins are grown in G phase and chromosomes are replicated in Due south stage. Post-obit this, four phases occur. Meiosis I is known every bit reductive division, every bit the cells are reduced from beingness diploid cells to being haploid cells.
1. Prophase I
Prophase I is the longest phase of meiosis, with three principal events occurring. The start is the condensation of chromatin into chromosomes that tin be seen through the microscope; the second is the synapsis or concrete contact betwixt homologous chromosomes; and the crossing over of genetic cloth betwixt these synapsed chromosomes. These events occur in v sub-phases:
- Leptonema– The get-go prophase consequence occurs: chromatin condenses to form visible chromosomes. Condensation and coiling of chromosomes occur.
- Zygonema– Chromosomes line up to form homologous pairs, in a process known as the homology search. These pairs are as well known as bivalents. Synapsis happens when the homologous pairs bring together. The synaptonemal circuitous forms.
- Pachynema– The tertiary main event of prophase I occurs: crossing over. Nonsister chromatids of homologous chromosome pairs commutation parts or segments. Chiasmata form where these exchanges take occurred. Each chromosome is now different to its parent chromosome only contains the same amount of genetic fabric.
- Diplonema– The synaptonemal complex dissolves and chromosome pairs begin to carve up. The chromosomes uncoil slightly to permit DNA transcription.
- Diakinesis – Chromosome condensation is furthered. Homologous chromosomes split up further but are still joined by a chiasmata, which moves towards the ends of the chromatids in a process referred to equally terminalization. The nuclear envelope and nucleoli disintegrate, and the meiotic spindle begins to form. Microtubules attach to the chromosomes at the kinetochore of each sister chromatid.
2. Metaphase I
Homologous pairs of chromosomes align on the equatorial airplane at the center of the prison cell. Contained assortment determines the orientation of each bivalent merely ensures that half of each chromosome pair is oriented to each pole. This is to ensure that homologous chromosomes practice not finish upward in the same cell. The arms of the sis chromatids are convergent.
3. Anaphase I
Microtubules begin to shorten, pulling one chromosome of each homologous pair to opposite poles in a procedure known equally disjunction. The sis chromatids of each chromosome stay connected. The cell begins to elongate in training for cytokinesis.
4. Telophase I
Meiosis I ends when the chromosomes of each homologous pair arrive at opposing poles of the cell. The microtubules disintegrate, 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 as interkinesis or interphase 2 happens in some organisms.
The Phases of Meiosis Two
Meiosis Two may begin with interkinesis or interphase Two. This differs from interphase I in that no S stage occurs, every bit the Deoxyribonucleic acid has already been replicated. Thus only a Chiliad phase occurs. Meiosis II is known as equational division, as the cells begin as haploid cells and end as haploid cells. At that place are once more four phases in meiosis Two: these differ slightly from those in meiosis I.
1. Prophase II
Chromatin condenses to grade visible chromosomes again. The nuclear envelope and nucleolus atomize, and spindle fibers begin to appear. No crossing over occurs.
two. Metaphase II
Spindle fibers connect to the kinetochore of each sister chromatid. The chromosomes align at the equatorial plane, which is rotated 90° compared to the equatorial plane in meiosis I. One sister chromatid faces each pole, with the arms divergent.
3. Anaphase II
The spindle fibers connected to each sister chromatid shorten, pulling one sis chromatid to each pole. Sister chromatids are known equally sister chromosomes from this point.
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 around each haploid chromosome fix, earlier cytokinesis occurs, forming 2 daughter cells from each parent jail cell, or four haploid daughter cells in total.
Figure 1. The phases of meiosis I and meiosis II, showing the germination of 4 haploid cells from a unmarried diploid cell.
How is Meiosis I Different from Meiosis II?
Meiosis is the production of 4 genetically various haploid daughter cells from one diploid parent cell. Meiosis can only occur in eukaryotic organisms. It is preceded by interphase, specifically the Yard phase of interphase. Both Meiosis I and II have the same number and organization of phases: prophase, metaphase, anaphase, and telophase. Both produce 2 girl cells from each parent prison cell.
However, Meiosis I begins with one diploid parent cell and ends with two haploid girl cells, halving the number of chromosomes in each cell. Meiosis Two starts with two haploid parent cells and ends with 4 haploid daughter cells, maintaining the number of chromosomes in each prison cell. Homologous pairs of cells are present in meiosis I and separate into chromosomes earlier meiosis Ii. In meiosis II, these chromosomes are further separated into sister chromatids. Meiosis I includes crossing over or recombination of genetic cloth between chromosome pairs, while meiosis Two does not. This occurs in meiosis I in a long and complicated prophase I, split into five sub-phases. The equatorial plane in meiosis II is rotated xc° from the alignment of the equatorial plane in meiosis I.
The table below summarizes the similarities and differences between meiosis I and meiosis 2.
Table 1. The similarities and differences between meiosis I and meiosis Ii.
| Meiosis I | Meiosis II |
Similarities | |
| Can merely occur in eukaryotes | |
| K phase of interphase ordinarily occurs showtime | |
| Production of daughter cells based on parent cell'southward genetic material | |
| Means of sexual reproduction in plants, animals, and fungi | |
| Four phases occur: prophase, metaphase, anaphase, telophase | |
Differences | |
| Starts as diploid; ends equally haploid | Starts as haploid; ends every bit haploid |
| Reductive division | Equational segmentation |
| Homologous chromosome pairs separate | Sister chromatids separate |
| Crossing over happens | Crossing over does not happen |
| Complicated division process | Simple segmentation process |
| Long duration | Short elapsing |
| Preceded by S-phase and G-stage | Preceded merely by G-stage |
| Sister chromatids in prophase have convergent arms | Sister chromatids in prophase have divergent arms |
| Equatorial plane is centered | Equatorial plane is rotated xc° |
| Prophase split into 5 sub-phases | Prophase does non have sub-phases |
| Ends with 2 girl cells | Ends with iv girl cells |
Why is Meiosis Important?
Meiosis is essential for the sexual reproduction of eukaryotic organisms, the enabling of genetic diversity 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 disease and survival of possible extinction events, as at that place volition always be sure individuals in a population ameliorate 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 product of haploid girl cells from diploid parent cells, using chromosomal reduction. These daughter cells are genetically singled-out from their parent cells due to the genetic recombination which occurs in meiosis I. This recombination is essential for genetic multifariousness within the population and the correction of genetic defects.
Meiosis I and 2 are similar in some aspects, including the number and arrangement of their phases and the production of two cells from a single cell. Yet, they too differ profoundly, with meiosis I being reductive segmentation and meiosis Ii being equational sectionalization. In this way, meiosis II is more than like to mitosis. Both stages of meiosis are important for the successful sexual reproduction of eukaryotic organisms.
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