Then the cell membrane can split the cytoplasm and organelles (termed cytokinesis). The events of mitosis describe the processes of splitting and moving nuclear DNA to opposite ends of the parent cell, where the nuclear membranes will reform.
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The DNA needs to be free from the nucleus so it can evenly distribute to two daughter cells. Remember that the DNA is in the nucleus, which is surrounded by the nuclear membrane. By observing the chromosome, one can identify the mitotic process. The stages of mitosis occur in sequence with specific events in each one. Significance of meiosisĪ) Helps to restore a constant diploid chromosomal constitution in a species at fertilization.Mitosis steps consist of prophase, metaphase, anaphase, and telophase the cell undergoes nucleus division and split into two identical daughter cells. Thus meiosis results into four daughter cells each having a haploid number of chromosomes. The chromatids become the chromosomes of the daughter cells they uncoil and regain their thread-like form. The nucleolus reappears and a nuclear membrane is formed around each set of chromatids. The sister chromatids separate and migrate to the opposite poles. They then orient themselves towards the opposite poles. New spindle fibres are formed.Ĭhromosomes migrate to the equator of the cell and attach to the spindle fibres at their centromeres. Once the first meiosis is complete, the daughter cells usually go into a short resting stage which is the interphase 2.Ĭhromosomes become shorter and thicker. In some organisms, telophase 1 does not exist no nuclear membrane is formed and the cells proceed directly into meiosis 2. The cell then divides into two across the middle. The spindle apparatus breaks down and a nuclear membrane is formed around each set of chromosomes. Once the chromosomes reach the poles, they become densely packed together. It is important to note that sister chromatids do not separate at this stage. This is because the spindle fibres shorten and thus the chromosomes are pulled. Homologous chromosomes separate and migrate to the opposite poles with their centromeres leading. Each pair of the homologous chromosomes moves to the equator of the spindle and attach to the spindles by their centromeres such that the two homologous chromosomes orientate towards opposite poles.
Nuclear membrane disappears completely making the chromosomes free in the cytoplasm. During synapsis, homologous chromosomes exchange genetic material between one another. Chromosomes may become coiled around each other and their chromatids may remain in contact at points called chiasmata. As prophase progresses, homologous chromosomes lie side by side and become intertwined rather like a zipper forming pairs called bivalents in a process called synapsis. This stage is manifested by the chromosomes becoming visible as distinct bodies as they get shorter and thicker and centrioles become arranged at opposite sides of the nucleus.
There is also a build up of energy to be used up in the meiotic process. Another important process that takes place is the formation of new cellular organelles. The chromosomes are not visible as discrete structures but instead, they appear as a diffuse tangle of threads called chromatin. One of the most important processes in this stage is chromosomal replication in which each chromosome produces an exact copy or replica of itself. Here are list of stages of meiosis 1 and meiosis 2 as below:ĭiscover What Occurs During the Meiosis Stages Meiosis 1 Phases Each stage is followed by 1 or 2 indicating whether it belongs to meiosis 1 or 2. Each of the two meiotic divisions is divided into interphase, prophase, metaphase, anaphase and telophase. Meiosis 2 results in separation the sister chromatids and for this reason, it is known as equatorial division. In meiosis 1, the number of chromosomes is reduced by one-half and for this reason, it is called reduction division. It consists of two successive divisions which are meiosis 1 and meiosis 2. Meiosis is the type of cell division that is seen during the formation of gametes (sex cells).
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