Synapsis happens when the homologous pairs join. Zygonema – Chromosomes line up to form homologous pairs, in a process known as the homology search.Condensation and coiling of chromosomes occur. Leptonema – The first prophase event occurs: chromatin condenses to form visible chromosomes.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. Prophase I is the longest phase of meiosis, with three main events occurring. Meiosis I is known as reductive division, as the cells are reduced from being diploid cells to being haploid cells. The Phases of Meiosis IĪfter Interphase I meiosis I occurs after Interphase I, where proteins are grown in G phase and chromosomes are replicated in S phase.
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. Different products are formed by these phases, although the basic principles of each are the same. 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. In each of these phases, there is a prophase, a metaphase, and anaphase and a telophase. Meiosis is then split into two phases: meiosis I and meiosis II. During the G phase proteins and enzymes necessary for growth are synthesized, while during the S phase chromosomal material is doubled. This is known as interphase, and can be further broken down into two phases in the meiotic cycle: Growth (G), and Synthesis (S). After chromosomal replication, chromosomes separate into sister chromatids. What Happens Before Meiosis?īefore meiosis, the chromosomes in the nucleus of the cell replicate to produce double the amount of chromosomal material. 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. Meiosis occurs in two distinct phases: meiosis I and meiosis II. This is why the chromosomal reduction is vital for the continuation of each species. This number would keep increasing with each generation. 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. The process of chromosomal reduction is important in the conservation of the chromosomal number of a species. 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 haploid cells produced by meiosis are germ cells, also known as gametes, sex cells or spores in plants and fungi. 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). Meiosis is how eukaryotic cells (plants, animals, and fungi) reproduce sexually.
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