 So, here topic, that is the fertilization and its type. So, what is the exact definition of fertilization and its different types. So, fertilization, it is the process, it is a biological process in which there is a fusion of gametes, the fusion of sperms and the eggs, the penetration of sperm into the egg and if there are haploid gametes, then after fertilization, there will be diploid zygote and it will develop into the complete individual. So, if we look at a natural process for the decision and an artificial process in which we are outside the body or within the lab in a test tube or in a petri plate or when we call it a test tube baby, then in these two processes, there is a very little difference, there is a very delicate difference and until all the conditions can be duplicated in the lab, then obviously fertilization cannot be done. So, all the prerequisites of fertilization are like a very delicate difference between these two cases. In both cases, diploid individuals formed. So, stages of fertilization process, the first thing is the preparation of sperm and eggs. When we talk about preparation, it means within the reproductive organs, the sperm formation or egg formation or this is usually as a result of myosin or haploid sperms or eggs. Then the sperm egg recognition is very important because those animals which are aquatic animals which have a water body in which there are more than one species that are living and responding to fertilization, then there will be attraction in the gametes of similar species and there will be recognition in them and this is a very intricate process. So, this sperm recognizes the egg of its own species and then it fuses or zygote formation happens. Then there is a fusion of sperm egg membranes. So, an egg membrane or sperm membrane, it becomes continuous. There is the formation of an aperture or a hole through which the nucleus of the sperm enters and then fuses with the egg nucleus. Then there is a penetration of sperm nucleus into the egg which we have talked about. So, then the fusion of the pro nuclei and the activation of the zygote and this pro nuclei are fused in this and the diploid number of chromosomes is attained and the zygote formation happens and then so this is again a stimulus for the mitosis to occur. So, a zygote which is one cell divides into two and this is the process of the mitosis and then there is an embryo formation and then there is further development. So, there are two types of that is the fertilization. There is external fertilization and internal fertilization. External fertilization is usually in aquatic animals, in fishes and in many other invertebrates. In eggs they are laid down, that is in water and at the same time the sperms they are sprayed on it and the fertilization occurs. So, this is what is called as external fertilization and then there is internal fertilization which is usually in terrestrial animals and in aquatic animals. So, in this type of fertilization the eggs are fertilized within the female reproductive tract. So, sperms they are introduced into the female tract and then there are eggs which come as ovulation results and there is the union of these two gametes and this zygote is formed. So, these are the types of fertilization, so this is all about.