Why Is Meiosis I Called Reduction Division?
Sexual propagation in living beings happens through the combination of male and female gametes, the sperm and the egg individually. Gametes are haploid in nature, i.e., they contain just a large portion of the quantity of chromosomes. This hereditary substance makes them unique in relation to other body cells. Meiosis prompts the arrangement of haploid cells. Let us have a point by point take a glimpse at meiosis 1 and the various stages and periods of meiosis 1. Mitotic cell division is equational in nature while meiosis is a decreasing division. The notable highlights of meiotic division that make it not quite the same as mitosis are as per the following:-
It happens in two phases of the atomic and cell division as Meiosis I and Meiosis II. DNA replication happens, nonetheless, just a single time.
It includes the matching of homologous chromosomes and recombination between them.
Four haploid girl cells are delivered toward the end, dissimilar to two diploid little girl cells in mitosis.
Meiosis 1 isolates the pair of homologous chromosomes and lessens the diploid cell to haploid. It is isolated into a few phases that incorporate prophase, metaphase, anaphase and telophase.
Meiosis 1 Stages
The various phases of meiosis 1 can be clarified by the accompanying stages :
Prophase 1
Metaphase 1
Anaphase 1
Telophase
Phases of Meiosis 1
The means paving the way to meiosis are like those of mitosis – the centrioles and chromosomes are repeated. The measure of DNA in the cell has multiplied, and the ploidy of the cell continues as before as in the past, at 2n. In meiosis I, the stages are practically equivalent to mitosis: prophase I, metaphase I, anaphase I, and telophase I (underneath figure). Meiosis I continues legitimately to meiosis II without experiencing interphase.
Meiosis I is novel in that hereditary assorted variety is produced through traverse and irregular situating of homologous chromosomes (bivalent chromosomes). What's more, in meiosis I, the chromosomal number is decreased from diploid (2n) to haploid (n) during this procedure. (See figure underneath, where meiosis I starts with a diploid (2n = 4) cell and finishes with two haploid (n = 2) cells.) In people (2n = 46), who have 23 sets of chromosomes, the quantity of chromosomes is diminished considerably toward the finish of meiosis I (n = 23).
Meiosis 1 Prophase 1
Prophase I is longer than the mitotic prophase and is additionally partitioned into 5 substages.
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
The chromosomes start to consolidate and accomplish a reduced structure during leptotene. In zygotene, the blending of homologous chromosomes begins a procedure known as chromosome synapsis, joined by the arrangement of an unpredictable structure called synaptonemal complex. A couple of synapsed homologous chromosomes shapes a complex known as bivalent or quadruplicate.
At the pachytene stage, traverse of non-sister chromatids of homologous chromosomes happens at the recombination knobs. The chromosomes stay connected at the destinations of traverse.
Diplotene denotes the disintegration of the synaptonemal complex and partition of the homologous chromosomes of the bivalents with the exception of at the destinations of traverse. The X-molded structures shaped during detachment are known as chiasmata.
Diakinesis is set apart by the end of chiasmata and gathering of the meiotic axle to isolate the homologous chromosomes. The nucleolus vanishes and the atomic envelope separates.
Meiosis 1 Metaphase 1
The bivalents adjust at the tropical plate and microtubules from the contrary posts join to the sets of homologous chromosomes.
Meiosis 1 Anaphase 1
The two chromosomes of each bivalent discrete and move to the furthest edges of the cells. The sister chromatids are joined to one another.
Meiosis 1 Telophase 1
The atomic layer returns and is trailed by cytokinesis. This offers access to a dyad of cells.
How to Start Learning the Meiosis I - Reductional Cell Division?
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FAQs on Meiosis I: The Process and Significance of Reduction Division
1. What is Meiosis I and why is it essential for sexual reproduction?
Meiosis I is the first of two major stages of meiotic cell division. It is known as the reductional division because it reduces the chromosome number of a diploid parent cell (2n) by half, producing two haploid daughter cells (n). This process is essential for sexual reproduction as it ensures the resulting gametes (sperm or egg cells) have the correct number of chromosomes, allowing for the restoration of the diploid state after fertilisation.
2. Why is Meiosis I specifically called the “reductional division”?
Meiosis I is called the reductional division because it is the stage where the actual reduction in chromosome number occurs. This happens during Anaphase I, where homologous chromosomes (one inherited from each parent) are separated and pulled to opposite poles of the cell. As a result, the daughter cells receive only half the number of chromosomes as the original parent cell, changing the ploidy level from diploid to haploid.
3. What are the key events that happen during Prophase I of Meiosis I?
Prophase I is the longest and most complex phase of Meiosis I, involving several critical events that are crucial for genetic diversity. The key events are:
Synapsis: Homologous chromosomes pair up to form structures called bivalents.
Crossing Over: Non-sister chromatids within a homologous pair exchange genetic material. This process, also known as recombination, creates new combinations of alleles.
Chiasmata Formation: The points where crossing over has occurred become visible as X-shaped structures called chiasmata, which hold the homologous chromosomes together until they are separated.
4. What is the primary significance of Meiosis I for a species?
The primary significance of Meiosis I lies in two main outcomes:
Maintenance of Chromosome Number: By halving the chromosome number to create haploid gametes, Meiosis I ensures that when two gametes fuse during fertilisation, the offspring will have the correct, stable diploid chromosome number for that species.
Creation of Genetic Variation: Through crossing over and the independent assortment of homologous chromosomes, Meiosis I shuffles genetic material, producing gametes with unique combinations of genes. This variation is the raw material for natural selection and evolution.
5. How does Meiosis I introduce genetic variation, while Meiosis II does not?
Meiosis I introduces genetic variation through two specific mechanisms. First, crossing over in Prophase I shuffles alleles between homologous chromosomes. Second, the independent assortment of these homologous chromosomes in Metaphase I ensures a random mix of parental chromosomes in the daughter cells. Meiosis II, in contrast, is an equational division where sister chromatids separate. Barring mutation, these sister chromatids are nearly identical, so their separation does not create new genetic combinations.
6. What is the fundamental difference in chromosome separation between Anaphase I of Meiosis and Anaphase of Mitosis?
The fundamental difference lies in what is being separated. In Anaphase I of Meiosis I, it is the homologous chromosomes that separate and move to opposite poles, while the sister chromatids remain attached at their centromeres. In contrast, during Anaphase of Mitosis, the centromeres themselves divide, and the sister chromatids are pulled apart to become individual chromosomes.
7. What would be the genetic consequence if a cell skipped Meiosis I but completed Meiosis II?
If a cell skipped Meiosis I and went directly to Meiosis II, the reduction of chromosome number would not occur. The diploid cell (2n) would enter Meiosis II, which would separate the sister chromatids. The resulting gametes would be diploid (2n) instead of haploid (n). If such a gamete participated in fertilisation, the resulting zygote would be triploid (3n), which in humans leads to severe developmental abnormalities and is usually not viable.
8. Can Meiosis I occur in haploid organisms?
No, Meiosis I cannot occur in organisms that are already haploid. Meiosis I is fundamentally defined by the pairing and separation of homologous chromosomes. Haploid organisms, by definition, have only one set of chromosomes and therefore lack homologous pairs. They can undergo mitosis to reproduce asexually, but meiosis is characteristic of the life cycle of sexually reproducing diploid organisms to produce haploid gametes.
