 fertilization, membrane and cortical events, first the contents, single fertilization, mark micro will lie around the sperm, ionic changes, fertilization membrane and the gray grescent formation. So first the single fertilization, sturophthagram simply see, the eggs normally one egg is fertilized by one sperm. The number of sperms that are approaching the egg is very high, so it is necessary to ensure that one egg is fertilized by one sperm. So normally one sperm fertilization will be good, it is a diploid, most of the animals carry 2n number of chromosomes, 1n is from the sperm and 1n is from the egg. So if one of the sperms fertilize, the complemented number of chromosomes will be disturbed, set of chromosomes. Like if two sperms enter, it will be 3n, so the organism of 3n will not survive in the case of animals, because most of the animals they are diploid, they carry 2n number. Like we are humans, so we get half of the chromosomes from our father, 23 chromosomes from the sperm of the father, that is one set, we call it 1n. So 1n from father, 1n from mother, it will be 2n, diploid number. So if one egg is fertilized by two sperms during fertilization, then what will happen is that if one egg and two sperms become 2n, then it will be 3n. So the development of the human being of 3n is not possible, it will not develop. So the critical thing of fertilization is to ensure that the human being of 3n can fertilize only one egg, which can be a zygote formation. Now normally, if we see in humans, in the case of humans, the time of fertilization for one egg, the accumulation of male sperms is in the number of millions. So many of the millions of sperms they reach to the egg. But the first thing that the egg will do successfully before fertilization is that it will share the zygote formation. When the next sperm is fertilized after one sperm, then the egg becomes inresponsive. The second sperm will not be able to penetrate the second sperm, so the second sperm will not be able to enter the second sperm. Now if we talk about the events, first of all, when the sperm approaches to the egg, you know that there is a vital membrane on the egg. On the vital membrane, the head of the sperms contains enzymes. When the enzyme is released, the vital membrane which is covered on the egg will hold the sperm and create a pore. And it will approach to the egg. As soon as the egg touches the plasma membrane, or it reaches close to the egg's plasma membrane, there are a lot of microvillages. So the microvillages encapsulate the sperm. They encapsulate the sperm. After which, the sperms are in the microvillages. There are contractile filaments in the microvillages. They withdraw or they withdraw the sperms from the egg. So this is a simple microvillage. The first sperm will approach the egg, the microvillages will surround it with its head, and after that it will be brought into the egg. Once the sperm enters into the egg, as soon as one egg enters into the egg, the second sperm blocks its entry immediately. The first event is that the membrane of the egg is reshuffled and changed immediately. As soon as these charges change, the membrane of the egg will not respond to the sperm. So the egg membrane will be irresponsible. It will not respond to the second sperm. When it does not respond to the second sperm, it can't enter into the egg. It will not be able to enter into the egg. The first event is that the reshuffle of the membrane on the charges takes place within milliseconds. This happens immediately. In a few milliseconds, the charges reshuffle. So that if a sperm is very close to the second sperm, it cannot enter again after the first sperm. The second event which blocks the double fertilization or second sperm's entry, that is actually the formation of fertilization membrane. To understand the fertilization membrane, if we look at the structure of the egg, the egg is a plasma membrane. And above the plasma membrane is the envelope of the egg which is called the white line membrane. The outer region of the cytoplasm of the egg contains specific granules which are called carticular granules. As soon as the first sperm enters, the carticular granules will ultimately reach the plasma membrane of the egg. The egg will go to the plasma membrane and it will discharge its material. The white line membrane and the plasma membrane of the egg are the space between them. Normally, the white line membrane is in contact with the plasma membrane. But as soon as the carticular granules discharge their material, the white line membrane will go a little further. The white line membrane and the plasma membrane will separate a little. We call the white line membrane the egg envelope. So what will happen to these two? Will they separate? And after that, as soon as the gap between the plasma membrane and the white line membrane comes, why is this gap here? Because the carticular granules have discharged their material. After that, on the next step, all the water molecules will come here. The water molecules will come and the result will be the gap between the white line membrane and the plasma membrane will be increased. So all the water molecules will fill the space between the white line membrane and the egg membrane. Then, the carticular granules have specific proteins that they have discharged here. Now what will they do with this protein? They will strengthen this white line membrane and will convert it into fertilization membrane. So the carticular granules and the material released here, they are all fibrous proteins. Fibrous proteins basically will provide the strength because of which the carticular plasma membrane and the white line membrane will become stiff and hard and ultimately convert into the fertilization membrane. And all these events will take place in one to two minutes. It will be completed. Look at this. This is the same event shown in a summarized form that we have the first sperm approaching. Look at these two sperms. The lower sperm will come slightly and touch the vital membrane. The next step is that the first sperm is surrounding the microvillage. With the surrounding of the microvillage you can see that the microvillage will completely surround it and it will be trapped and it will be taken into one. With the egg, for fusion, if we look at the fourth picture, the sperm has entered the egg. But along with this, we have a second sperm in the first picture, the second and third pictures. So the second sperm we have the reasons for that. Number one, the charges of the membrane Number two, the particular granules make the fertilization membrane. And along with that, the microvillage won't respond to the second sperm. The last event of fertilization, after the fertilization, when the sperm enters, the egg's cytoplasm will start streaming movements. Especially the outer cytoplasm, the area near the cell membrane, the cytoplasm will start streaming which is also called cyclosis. Due to this streaming movement, it will further block the entry of the second sperm. The benefit of the streaming movement is that it will make the gray crescent. Gray crescent is very important in the developmental process. The development of gray crescent and the second important is that as the streaming movement starts, the development process will start due to the start of the streaming movement.