 Now, we talk about sexual reproduction in animals. In animals, sexual reproduction also occur just like plants to fertilization of gametes which are called the sperms and the ova. Sperms in the case of males and ova in the case of females. Gametes are produced in the animals just like all other organisms by the process of meiosis. We know that meiosis is reduction division. What is when meiosis occur, one cell which is a germline cell as we described it, all of the body cells they do not have ability to undergo meiosis. Only the germ cells have the capability to undergo meiosis. When they undergo meiosis, they divide into that is one cell, one germ cell is divided into four haploid cells. That is every cell have a haploid set of chromosomes, half number of chromosomes. Females and males, they are usually different in only one pair of chromosomes. For example, human beings have 46 chromosomes which are in 23 pairs, 22 pairs are called the autosomes. These pairs just alike in both males and females, but the 23rd pair is different. Females have both X chromosomes in the 23rd pairs which are just like each other, just like all other homologous chromosomes, but the males have in this 23rd pair, one chromosome different from the other, one is just like an X, but the other is a smaller chromosome which is called Y, which have fewer genes, but which have some specific genes which causes the organism to become a male that is different from the female organism. So males and females, they are usually physically different from each other and this is actually due to the specific type of chromosomes. Frogs for example, they carry out sexual reproduction. Female frogs, they have a set of ovaries which produces large number of ova as we know that frogs are the organisms which are part of the group called amphibia. In amphibia the organism which are called transition between the aquatic and the land animals. So frogs, they spend some part of their life in water and some other part of their life in on land. For reproduction frogs go to the water. Frogs, the female frogs, they have set of ovaries which produces large number of ova and they go to the water and release these ova into the water. The male frogs, they have testis which produces spams. These spams, these are laid down on the ova. Fertilization takes place in water and sperm and ova, they join together to form a zygote. This zygote then now have a 2N number of chromosomes because sperm have a N number of chromosome and ovum have a N number of chromosome. When they join they make a zygote. Zygote have 2N number of chromosomes that is normal number of chromosomes and zygote then divides by mitosis into a stage of life of the frog called larva. Larva is an actively feeding stage. It feeds upon the different types of organisms present in water. For example, some types of larvae, mosquito larvae, phytoplankton, zooplankton and others and they grow actively. After some time they are converted into biophosphic process carmorphogenesis. They are converted into adult frog when they are grown quite well. This also takes place by the sexual means that is males and females, both organisms are involved. Human reproduce sexually by fertilization of gametes called sperms and ova. Males produces sperms and the females produces ova. Sperms and ova are called gametes. Gametes are produced by specialized organs called testis and ovaries. Testis in males and ovaries in females. Gametes, as all of other organisms, have a haploid number of chromosomes. Or we can also say a haploid set of chromosomes that is 23 chromosomes are present in each gamete. 22 of these pairs are alike but the 23rd one is different in males and females. Females have all the 22 autosomal chromosomes and an X chromosome. But the males, we call them a heterogametic sex because they have in some of these gametes 22 autosomes and one X or 22 autosomes and one Y. So, females always contribute an X. Males contribute either an X or Y. So, the gender of the child is determined by the male gamete and not by the female gamete. Female gamete always contribute an X. If male gamete have an X, then two X will be complete and a female child will be produced. If the male gamete have a Y chromosome, then the autosomal pairs will be 22 and the 23rd pair will be XY and a male child will be produced. So, it depends upon the male chromosome that whether it have an X or a Y, that female or male child will be produced. Now, the basic components of the male reproductive system in human beings. One male reproductive system consists of a pair of gonads called testis and a system of accessory tubules. Testis T-E-S-T-I-S when we say it is for singular and when we add an E, that is T-E-S-T-E-S, it is plural, that is used for two. Testis are paired, that is two are present. These produces spams. Testis lie outside the body in a sac called scotum because spermatogenesis is a process which is highly sensitive to temperature. So these are present, testis are present outside so that temperature is lower. From testis, sperms are transferred to the main duct called vas deferens. Vas deferens is a duct that is later on make a complex system of ducts. Vas deferens makes a complex system of ducts upon the surface of testis called epididymis. From epididymis, sperms are transferred through gerinogenital duct and then they are discharged. Function of the testis. Testis produces spams. This is their first function. The second function is that they produce a hormone called testosterone. Testosterone is a hormone that produces all the male-like characteristics in an organism. For example, testosterone is a very strong anabolic hormone. It affects all the muscles of the body and the muscles. They grow better. This is the reason that males usually have more muscles in comparison to female and they have more stronger muscles in comparison to the females because females do not have this hormone. Testosterone also affect many other characteristics like the beard on the face is also enhanced or we can say produced by the effect of testosterone. Testosterone also affect the process of sperm metagenesis that is sperm production. Testis consists of a system of tibules. This system is called these tibules are called semineferrous tibules. These tibules there is a epithelium there are different types of cells. It's from its germinal epithelium that is from its germ cells primary spermatocytes are produced. Germ cells actually we call them germinal epithelium they divide by mitosis to produce primary spermatocytes. Primary spermatocytes have a 2n number of chromosomes because they are divided by mitosis of sperm mother cells called spermatogonia. Then primary spermatocytes which have 2n number of chromosomes they undergo meiosis and they produces secondary spermatocytes which have an n number of chromosomes. Secondary spermatocytes further divides and they make spermatoids. These spermatoids are actually now 4 because they are produced from secondary spermatocytes which have n number of chromosomes they also have a n number of chromosome or haploid set of chromosomes. Spermatoids then divide then by morphological changes are produced into sperms. Testis also have some large cells called sertoli cells. These sertoli cells nourish the sperms the developing sperms they're developing stages and they also provide surface and protection to the developing sperms in the seminiferous tibules. When these sperms are mature when they become mature they are released into the lumen of the seminiferous tibules from where they move towards the vas deferens. Here this process is exemplified by a diagram you can see that from spermatogonia or the sperm mother cells by mitosis they are divided into primary spermatocytes which have a 2n number of chromosomes. Then meiosis takes place and secondary spermatocytes are formed after first meiotic division and after second meiotic division that occur in both of the secondary spermatocytes four spermatoids are formed. And these four spermatoids are then modified by different morphological changes into the active sperms. Now we talk about the female reproductive system. Female reproductive system consists of a pair of ovaries and associated system of tubes. Ovaries lies inside the body in the body cavity and the function of ovaries is to produce ova and to produce some hormone. Ovaries leads to the tubes called oviducts. Oviducts are also called the filopian tubes sometimes. Oviducts open into the uterus, ovum is fertilized into the oviducts. Then moves to the uterus where it is implanted. If it is fertilized then it moves towards the uterus and implanted here. Implanted mean that it attaches to the wall of the uterus and a placenta. Connection is established between the uterine tissues and the tissues of the embryo for the exchange of materials. Uterus is then connected to the vagina through cervix. Now we talk about function of the ovaries. Function of the ovaries is to produce ova and female hormones called estrogen progesterone. Estrogen and progesterone are the hormones which affects different processes of female and develop female-like characteristics. Now we talk about the process of ogenesis. Germ cells in the ovary, just like the testis, ovaries also have some cells called germ cells. Not all the cells of ovaries cannot produce an ovum. The germ cells only can produce the ovum. Just like in the testis, the germ cells divide by mitosis into primary oocyte, which have a two N number of chromosomes. That is because it is divided by mitosis, it have the same number of chromosomes as the parents do have. Then the primary oocyte divides by meiosis. Meiosis occur in the primary oocytes. They are converted to secondary oocyte. Secondary oocyte, because it is produced by meiosis, the first or the first meiotic division of the meiosis, they also have a haploid set of chromosomes. That is half number of chromosomes. There is a difference between the male and the female division of gametes. We talk about it later. Then from secondary oocytes, two more cells are produced. Three are called polar bodies and one is called ova. Now we look at the diagram to clarify the process. We look at the diagram. First cell, which is shown, is the ogonium. It is produced into primary oocyte because mitosis occur in the ogonium. The result is a primary oocyte, which have a 2n number of chromosomes. Then primary oocyte divides by meiosis 1 and because it is divided by meiosis 1, which is a reduction division, it is converted into two haploid cells. But here is a difference. One cell is larger than other cell. As you can see the diagram, the secondary oocyte, one cell is very large and the other cell is very small. The large one is called a secondary oocyte and the other one is called a polar body. What is the difference between two? Secondary oocyte have large quantity of cytoplasm and a half set of chromosomes. But the polar body have a half set of chromosomes but it have very small quantity of cytoplasm. Then the second meiotic division takes place in secondary oocyte and in this polar body we call it a first polar body. When secondary oocyte is divided into two by meiotic division, it makes an ovum or an egg and another polar body. That is by meiosis 2, one ovum is produced or egg is produced and the other polar body is produced. Again there is a same difference. That is ovum have a large quantity of cytoplasm and the polar body have small quantity of cytoplasm. The first polar body also divide by the same way by meiosis 2 into two polar body. All of these polar bodies they are actually wasted away and only the ovum which is produced is used in further process of fertilization and making the cygo. So actually in a male from one cell four spams are produced but in females from one cell one ovum and three polar bodies are produced. Three are wasted away and one only is used. When this is released from the ovary, egg is released from the ovary we call this process ovulation. This was about the reproductive systems in different types of organisms. We talked about that why reproduction is important. We talked about different methods of reproduction, asexual reproduction which occur by various methods. Then we talk about the sexual reproduction in plants, in particularly higher plants in animals and in human beings.