This is to ensure that homologous chromosomes do not end up in the same cell. Independent assortment determines the orientation of each bivalent but ensures that half of each chromosome pair is oriented to each pole. Homologous pairs of chromosomes align on the equatorial plane at the center of the cell. Microtubules attach to the chromosomes at the kinetochore of each sister chromatid. The nuclear envelope and nucleoli disintegrate, and the meiotic spindle begins to form. 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. Diakinesis – Chromosome condensation is furthered.The chromosomes uncoil slightly to allow DNA transcription. Diplonema – The synaptonemal complex dissolves and chromosome pairs begin to separate.Each chromosome is now different to its parent chromosome but contains the same amount of genetic material. Chiasmata form where these exchanges have occurred. Nonsister chromatids of homologous chromosome pairs exchange parts or segments. Pachynema – The third main event of prophase I occurs: crossing over.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 second is the synapsis or physical contact between homologous chromosomes and the crossing over of genetic material between these synapsed chromosomes. First chromatin condenses in 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 diploid cells to haploid cells. Meiosis I occurs after Interphase I, where proteins are grown in the G phase and chromosomes are replicated in the S phase. Meiosis I is preceded in interphase by both the G phase and S phase, while meiosis II is only preceded by the S phase chromosomal replication is not necessary again. Different products are formed by these phases, although the basic principles of each are the same. On the other hand, in meiosis II they are known as prophase II, metaphase II, anaphase II, and telophase II. In meiosis I these are known as prophase I, metaphase I, anaphase I, and telophase I. In each of these phases, there is a prophase, a metaphase, an anaphase, and a telophase. Meiosis is then split into two phases: meiosis I and meiosis II. Meanwhile, during the S phase, chromosomal material is doubled. During the G phase proteins and enzymes necessary for growth are synthesized. Interphase 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. Each phase produces different products and is as crucial to the production of viable germ cells.

There are many similarities and differences between these phases. Meiosis occurs in two distinct phases: meiosis I and meiosis II. This is why chromosomal reduction is vital for the continuation of each species. This number would keep increasing with each generation. If chromosome numbers were not reduced, 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 are germ cells, also known as gametes, sex cells, or spores in plants and fungi. It is a process of chromosomal reduction in which a diploid cell (with two complete and identical chromosome sets) forms haploid cells (with only one chromosome set). Meiosis is how eukaryotic cells (plants, animals, and fungi) reproduce sexually. Meiosis I and Meiosis II Biology Review.How is Meiosis I Different from Meiosis II?.

Mitosis vs meiosis differences