However, the bivalent structure is not broken as the two chromosomes remain tightly linked at chiasmata points. This is known as chiasmata.ĭuring this phase, the homologous chromosomes undergo uncoiling and are visible as two threads. This process is called crossing-over.Ī physical link is formed between the non-sister chromatids through which the crossing-over takes place. It is the process during which the non-sister chromatids can exchange their segments resulting in genetic variations. Once the pairing process is complete, the homologous recombination takes place. It results in the formation of tetrad chromosomes (called so because of four sister chromatids) also known as bivalent (two chromosomes). The pairing of homologous chromosomes is completed during this phase. A total of 46 chromosomes, each having 2 chromatids can be seen in the nucleus towards the end of this phase.ĭuring this phase, the homologous chromosomes come close to each other to form homologous pairs.
Each chromosome consists of two sister chromatids.
It is further divided into five phases.ĭuring this phase, the chromosomes start appearing as thin threads within the nucleus. It is the longest phase of meiosis I during which the nuclear envelope disappears, and genetic exchange takes place.
G 2 phase, the cell makes proteins that are needed for meiosisĪfter the G 2 phase is complete, the cells enter Prophase I. S phase, the cell undergoes DNA replication. G 1 phase, the cell grows in size and makes necessary proteins in this phase. The interphase is divided into three phases there is no interphase between Meiosis I and Meiosis II. It is the phase during which a cell prepares itself for division. The detail of all these phases is given below. Meiosis I is preceded by interphase during which the cell prepares itself for meiosis. Meiosis I is divided into the following four phases It should be kept in mind that normal cells have only 23 pairs of chromosomes as they have not undergone DNA replication. Thus, chromosomes are present in the form of homologous pairs, each cell having 46 pairs of chromosomes at the beginning of Meiosis I. This is because the cells have undergone DNA replication before entering Meiosis I. The process of meiosis begins with the diploid cells having double the number of chromosomes. This is the reason why DNA and the number of chromosomes are halved after each meiosis. Meiosis I is immediately followed by Meiosis II without any intervening interphase. The DNA replication takes place only before meiosis I. these two rounds of cell division are called Meiosis involves two rounds of cell division giving rise to four daughter cells. Read more about the Meiotic Cell Cycle Phases of Meiosis In this article, we will study different phases of meiosis, its significance in the human body, and its difference from mitosis. It only takes place in cells that actively participate in sexual reproduction i.e. Meiosis is only seen in organisms that undergo sexual reproduction. It is a type of cell division in which one parent cell is divided into four daughter cells, each having half the number of chromosomes as compared to the parent cell. These cells that take part in sexual reproduction are called gametes and the process that divides the chromosomes into two halves is called meiosis. To ensure that the same number of chromosomes are transferred to the next generation as present in the parents, the nuclear material should be first divided into two halves before the fusions of cells. This zygote is formed after the fusion of one cell from each parent. In organisms that reproduce through sexual reproduction, the new organism is developed from a single cell called a zygote. 
Each pair is homologous containing two identical chromosomes except the sex chromosomes that are different in males and females. Which cells undergo meiosis in females?Īll the organisms in a species have an equal number of chromosomes in their cells that are present in the form of pairs.What is the difference between meiosis and mitosis?.
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