What the difference between meiosis and meitosis process. Six pont
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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 means a cell with two complete and identical chromosome sets) is reduced to form haploid cells (these are cells with only one chromosome set). 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 form a diploid zygote, which grows to form another functional adult of the same 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, then the resulting offspring would have a tetraploid chromosome set: that is, it 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 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 phase being as crucial to the production of viable germ cells.
What Happens Before Meiosis?
Before meiosis, the chromosomes in the nucleus of the 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 be further broken down into two phases in the meiotic cycle: Growth (G), and Synthesis (S). During the G phase proteins and enzymes necessary for growth are synthesized, while during the S phase chromosomal material is doubled.
Meiosis is then split 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 as 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 G phase and S phase, while meiosis II is only preceded by S phase: chromosomal replication is not necessary again.
The Phases of Meiosis I
After Interphase I meiosis I occurs after Interphase I, where proteins are grown in G phase and chromosomes are replicated in S phase. Following this, four phases occur. Meiosis I is known as reductive division, as the cells are reduced from being diploid cells to being 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 can be seen through the microscope; the second is the synapsis or physical contact between homologous chromosomes; and the crossing over of genetic material between these synapsed chromosomes. These events occur in five sub-phases:
Leptonema – The first prophase event 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 also 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 now different to its parent chromosome but contains the same amount of genetic material.
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 but 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 chro
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meiosis occurs in reproduction while meitosis occurs in somatic cell