 Meiosis is also called a reduction division because chromosome numbers become one-half in each daughter cell. Meiosis consists of two stages, meiosis one and meiosis two. In meiosis one actually, meiosis one is technically the reduction division because during meiosis one the chromosome number becomes one-half and two daughter cells are formed from one mother cell. The meiosis two occur in both of these daughter cells separately and both of these daughter cells each one divides into two further. So ultimately at the end of meiosis we have four daughter cells but the division the actual reduction division in which chromosome number reduced to one-half is the meiosis one. Meiosis two is just like that of mitosis. Now we talk about meiosis one. Meiosis one consists of a prophase, we call it prophase one because this is the prophase of the meiosis one, metaphase one, anaphase one, telophase one and a cytokinesis. When the cell divides into two then when the nuclear division is complete then the cell divides into two by cytokinesis and when it is almost divided it starts its next phase of division called meiosis two. Meiosis two is just like the mitosis it simply divides both the cells into equal to same type of cells with equal number of chromosomes. Now we look at the detailed process of meiosis. Meiosis one consists of prophase then metaphase then anaphase then a telophase we look at first of all the prophase one. As we know that the chromosomes they are just like mitosis they are already duplicated. It means that every chromosome have two sister chromatids it is doubled in the number. As you can see in the diagram there are two homologous chromosomes which are shown. Each chromosome which is now called each homologue each homologue will consist of actually two sister chromatids. You can see one in green and the other in blue. The green one is one homologue that is one chromosome which is duplicated. The blue one is its homologous partner and which is in its appearance just like that of the first one which is shown in blue color and this also consists of two sister chromatids. Now what happen in the prophase one as is shown in the second diagram the prophase one is the longest phase of meiosis. In this phase actually the homologous chromosomes they pair up with each other. They come close together and some of their parts are attached to each other to make the structures called kiasmeta. In the diagram the second diagram you can see a single kiasma in which one part of homologue one is attached with the or we can say crossed with the part of the homologue two. We call this process peering up or synapses. We say that these chromosomes the homologous they are synapsed together but remember at this stage that only the homologous chromosomes will pair up with each other. As we know that in human beings for example they have 46 chromosomes and there will be 23 pairs. The chromosomes in one pair only will make kiasmeta with each other. One homologous chromosome will not pair up with any other homologous set. They will only pair up with their own type. If they do so wrongly that will be an error in the meiosis which may result in a problem later on. So usually or normally homologous chromosomes pair up with each other. We call them these peering synapses. Now what is the purpose of this peering? Purpose of this peering is recombination. These parts of chromosomes which pair up which are crossing each other what will happen that these parts both of these parts will break up from the original chromosome and will attach to the other homolog. As you can see in the bottom of the diagram now the two homologs are shown but you can see that the homolog on the top in the green color have a small part of blue color which is actually broken up during the kiasmeta during the synapses from the homolog to and attach to the homolog one. Same happened with the homolog two. You can see in the last part of the diagram that the one part of homolog two looks like green because actually this is the part of homolog one which was during kiasmeta for machine again the peering up broken up and attaches to the homolog two. Now you see that both of the chromosomes they have a large part of each other. They exchanged their parts. We say that they exchanged their DNA or nuclear material. The result of this situation is new recombinations. There are new sets of genes which are formed and the result will be new characteristics which will appear in the organism. This is the most important property and advantage of the sexual reproduction that during the meiosis process the chromosomes they do recombine and as we know as many chromosomes as an organism have as many recombinations it can form and every recombination may result into a different characteristic which gives an evolutionary advantage to that particular organism. So meiosis this is the prophase one is one of the most important parts of meiosis. These paired chromosomes which are making pair as you can see in the diagram on the top these chromosomes homologs which are paired the homolog one and homolog two collectively are called sometimes bivalents or tetrads. They are called bivalents because both homologs are attached with each other. They are called tetrads because we know that due to duplication or the replication each homolog consists of now two sister chromatids. So in total they are making four chromosomes. We call them tetrads or sometimes we call them bivalents. At till end of the prophase one lot many recombinations like this are formed constituted because almost every homologous pair pair up with each other and they exchange their different parts so lot many recombinations they are formed. With this all the other features of the prophase they also takes place. The spindle fibers are formed because chromosomes have to attach to spindle fibers to move from their place from the center towards the poles. So spindle fibers are formed in animal cells, centrioles will do it. In plant cells spindle fibers will be formed by other methods and the nuclear membrane ultimately and almost end of this phase will disappear and now there is one more important difference. Now the each homologous pair is attached with each other by one kinetochore. There is one kinetochore for each homologous pair which is in contrast to mitosis in which there is one kinetochore for one sister chromatid. Now both sister chromatids of one homolog are attached with only one kinetochore and this is very important because we know that meiosis is the reduction division and one homolog have to go to one pole and the other homolog have to go to the other pole. Now we know that at about end of the prophase spindle fibers which are already formed each homolog attaches to the spindle fibers with its kinetochore. Now because there is one kinetochore per homolog so every homolog as a whole is attached to a spindle fiber which is the same as true for the other homolog. There is one more important thing as we know that every organism which is sexually reproduced always have one set of chromosomes coming from the mother and the other set coming from the father. The homologs which are coming from mother and father they are arranged in different orientations that is in one pair for example the maternal homolog will be on one side towards one pole and the paternal homolog will be on the other side. This is different for each chromosome. It means that in a gamete there are about 50-50 chances that the gamete will have a maternal homolog or a paternal homolog which is also a very important feature for we can say new recombination. And at the end of when the spindle fibers are formed the chromosomes they attach the nuclear membrane is dissolved or start disappearing and it is disappeared at the end of very very long phase the pro phase one and then the pro phase one ends. When the pro phase one ends the next phase starts that is meta phase one because this is part of the meiosis one. Now in the meta phase one the chromosomes the homologs they are attached on the spindle fibers arrange themselves on the equator. All of the homologs are arranged on the equator almost in a rough straight line or in rough circular we can say part. And after the meta phase one comes the n-phase one. Now n-phase one is very very important because in this n-phase one of the meiosis the chromosomes have to move towards the pole and now half chromosomes have to go to one pole and the half chromosomes have to go to the other pole. What happened that because we know that there was one kind of core per homolog per two sister chromatids. It means that the two sister chromatids are going to move towards one pole and the other two sister chromatids are going towards the second pole. Now the microtubules or the spindle fibers they start pulling the chromosomes towards the poles of the cell and now because again I repeat the same thing because there is one kind of core per two sister chromatids of one homolog so one homolog which consists of now two sister chromatids will move towards one pole and the other homolog we can call here homolog two which also consists of two sister chromatids will move towards the other pole. So the half set of the chromosomes is moving towards one pole and the other half set is moving towards the second pole. So this is the n-phase one. Now this stage is extremely important because if there is a slight error in this phase it results into an unequal distribution of the chromosomes in the gametes and if there is an unequal distribution of chromosomes in the gamete it result in very very serious disorders. When the n-phase finishes the chromosomes are moving towards poles almost they are reaching near poles. The last stage of meiosis one starts that is called the telophase one. In telophase one the half number of chromosomes reached at one pole the other half of chromosomes half set has reached at the second pole and now the nuclear membrane starts forming the chromatin material start slightly decondensing. With this the meiosis one or the nuclear division one of meiosis is complete and then the cell is divided into two cells in again just like in plant cells by a phragmoplast and in animal cells by a cleavage formation. Cell is divided into two. Now there is a slight difference from mitosis that what happened that sometimes the cells are completely divided into two. When they are just dividing at the end of their cytokinesis they just start their second nuclear division which is called meiosis two because meiosis is a continuous process. So what happened that when the nuclear division is complete cleavage pharaoh is formed and cleavage pharaoh almost reaches at the end then the next nuclear division just starts. We call it meiosis two. Now we have a look on a diagram which explains the meiosis one. If we look at the diagram the first part shows the interface one. When the cell is at interface its chromosomes a chromatin material is not very visible and it is showing centrosome a pair of centrioles. The next diagram towards right as you can see that the chromosomes the homologous pairs they consist of two sister chromatids each and they are forming chiasmata. Now here in this diagram you can observe that per homolog more than one chiasmata could be formed. You can see in the small sized chromosome pair the homolog pair there is one chiasmata but you can see the chromosome which is larger one there are two chiasmata. So it means there may be more than one chiasmata per homologous pair. Then comes the next stage the metaphase one. In the metaphase one as we talked about it in it the chromosomes are arranged in the equatorial plate in the center but now each homolog is attached with the kinetochore to the microtubules the spindle fibres and not sister chromatids. In metaphase one you can see that the whole homolog the complete chromosomes with its both sister chromatids is moving towards the poles and you can observe various recombinations present in these chromosomes which are going towards the poles. Then comes the tera phase to start decondensing nuclear membrane starts appearing in the cell divides.