The Nucleus Divides in Meiosis I and Again in Meiosis Ii True False
Recap: 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 jail cell (this means a jail cell with two consummate and identical chromosome sets) is reduced to form haploid cells (these are cells with only one chromosome fix). 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: ii germ cells combine to form 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 not reduced, and a diploid germ prison cell was produced by each parent, and then the resulting offspring would take a tetraploid chromosome set: that is, information technology would have four identical sets of chromosomes. This number would keep increasing with each generation. This is why the chromosomal reduction is vital for the continuation of each species.
Meiosis occurs in 2 distinct phases: meiosis I and meiosis II. There are many similarities and differences between these phases, with each phase producing unlike products and each phase being as crucial to the production of feasible germ cells.
What Happens Before Meiosis?
Before meiosis, the chromosomes in the nucleus of the cell replicate to produce double the corporeality of chromosomal material. After chromosomal replication, chromosomes split into sister chromatids. This is known every bit interphase, and tin be further broken down into 2 phases in the meiotic cycle: Growth (M), and Synthesis (S). During the G stage proteins and enzymes necessary for growth are synthesized, while during the S stage chromosomal fabric is doubled.
Meiosis is and so split into two phases: meiosis I and meiosis 2. In each of these phases, at that place 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 same. Also, meiosis I is preceded in interphase by both Yard phase and S phase, while meiosis II is only preceded by S phase: chromosomal replication is non necessary again.
The Phases of Meiosis I
Afterwards Interphase I meiosis I occurs after Interphase I, where proteins are grown in G phase and chromosomes are replicated in S phase. Following this, iv phases occur. Meiosis I is known every bit reductive sectionalization, as 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 main events occurring. The outset is the condensation of chromatin into chromosomes that tin exist seen through the microscope; the second is the synapsis or concrete contact betwixt homologous chromosomes; and the crossing over of genetic material between these synapsed chromosomes. These events occur in five sub-phases:
- Leptonema– The first prophase outcome occurs: chromatin condenses to form visible chromosomes. Condensation and coiling of chromosomes occur.
- Zygonema– Chromosomes line up to class homologous pairs, in a procedure known as the homology search. These pairs are as well known equally bivalents. Synapsis happens when the homologous pairs join. The synaptonemal complex forms.
- Pachynema– The 3rd main effect of prophase I occurs: crossing over. Nonsister chromatids of homologous chromosome pairs exchange parts or segments. Chiasmata course where these exchanges have occurred. Each chromosome is now unlike to its parent chromosome but contains the same amount of genetic cloth.
- Diplonema– The synaptonemal complex dissolves and chromosome pairs begin to separate. The chromosomes uncoil slightly to allow DNA transcription.
- Diakinesis – Chromosome condensation is furthered. Homologous chromosomes separate further only are still joined by a chiasmata, which moves towards the ends of the chromatids in a process referred to as 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 plane at the center of the cell. Independent array 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 do not terminate upwardly 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 process known as disjunction. The sister chromatids of each chromosome stay connected. The cell begins to elongate in grooming for cytokinesis.
four. Telophase I
Meiosis I ends when the chromosomes of each homologous pair arrive at opposing poles of the prison cell. The microtubules atomize, and a new nuclear membrane forms around each haploid set of chromosomes. The chromosomes uncoil, forming chromatin once more, and cytokinesis occurs, forming 2 non-identical daughter cells. A resting phase known as interkinesis or interphase 2 happens in some organisms.
The Phases of Meiosis II
Meiosis 2 may begin with interkinesis or interphase Two. This differs from interphase I in that no S phase occurs, every bit the Deoxyribonucleic acid has already been replicated. Thus but a K phase occurs. Meiosis Two is known as equational division, equally the cells begin as haploid cells and stop as haploid cells. At that place are again 4 phases in meiosis 2: these differ slightly from those in meiosis I.
one. Prophase Two
Chromatin condenses to form visible chromosomes again. The nuclear envelope and nucleolus disintegrate, and spindle fibers begin to appear. No crossing over occurs.
2. 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. 1 sister chromatid faces each pole, with the arms divergent.
three. Anaphase 2
The spindle fibers connected to each sis chromatid shorten, pulling 1 sister chromatid to each pole. Sis chromatids are known as sister chromosomes from this point.
iv. Telophase II
Meiosis II ends when the sis chromosomes accept reached opposing poles. The spindle disintegrates, and the chromosomes recoil, forming chromatin. A nuclear envelope forms around each haploid chromosome prepare, before cytokinesis occurs, forming two daughter cells from each parent cell, or four haploid daughter cells in total.
Figure 1. The phases of meiosis I and meiosis Ii, showing the formation of 4 haploid cells from a unmarried diploid prison cell.
How is Meiosis I Different from Meiosis II?
Meiosis is the product of four genetically diverse haploid daughter cells from i diploid parent cell. Meiosis can just occur in eukaryotic organisms. It is preceded past interphase, specifically the Yard phase of interphase. Both Meiosis I and II accept the same number and arrangement of phases: prophase, metaphase, anaphase, and telophase. Both produce two daughter cells from each parent cell.
All the same, Meiosis I begins with ane diploid parent cell and ends with two haploid daughter cells, halving the number of chromosomes in each cell. Meiosis 2 starts with two haploid parent cells and ends with four haploid daughter cells, maintaining the number of chromosomes in each cell. Homologous pairs of cells are present in meiosis I and split up into chromosomes before meiosis 2. 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 not. This occurs in meiosis I in a long and complicated prophase I, split into v sub-phases. The equatorial plane in meiosis II is rotated 90° from the alignment of the equatorial plane in meiosis I.
The table beneath summarizes the similarities and differences between meiosis I and meiosis II.
Table one. The similarities and differences betwixt meiosis I and meiosis Two.
| Meiosis I | Meiosis II |
Similarities | |
| Can merely occur in eukaryotes | |
| G phase of interphase commonly occurs first | |
| Production of daughter cells based on parent cell'southward genetic cloth | |
| Means of sexual reproduction in plants, animals, and fungi | |
| Four phases occur: prophase, metaphase, anaphase, telophase | |
Differences | |
| Starts as diploid; ends equally haploid | Starts equally haploid; ends as haploid |
| Reductive partition | Equational sectionalization |
| Homologous chromosome pairs split up | Sister chromatids divide |
| Crossing over happens | Crossing over does not happen |
| Complicated sectionalization process | Simple division procedure |
| Long duration | Curt duration |
| Preceded by South-phase and G-phase | Preceded only past Yard-phase |
| Sis chromatids in prophase have convergent artillery | Sister chromatids in prophase have divergent artillery |
| Equatorial plane is centered | Equatorial plane is rotated 90° |
| Prophase split into five sub-phases | Prophase does not have sub-phases |
| Ends with two daughter cells | Ends with 4 girl cells |
Why is Meiosis Of import?
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 diverseness of a species. This provides a buffer against genetic defects, susceptibility to affliction and survival of possible extinction events, as there will always be certain individuals in a population meliorate able to survive changes in environmental condition. Recombination farther allows genetic defects to be masked or fifty-fifty replaced by healthy alleles in offspring of diseased parents.
Meiosis I and Meiosis II Biological science 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 multifariousness inside the population and the correction of genetic defects.
Meiosis I and II are like in some aspects, including the number and organization of their phases and the production of two cells from a single cell. Even so, they likewise differ greatly, with meiosis I being reductive division and meiosis II being equational partition. In this way, meiosis 2 is more similar to mitosis. Both stages of meiosis are important for the successful sexual reproduction of eukaryotic organisms.
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