describe the process of sexual reproduction in animals with diagram.
Answers
Sexual reproduction is the production of a new organism from two parents by making use of their sex cells or gametes. The humans, fish, frogs, cats and dogs, all reproduce by the method of sexual reproduction.It is important to know the meaning of some important terms like male sex, female sex, gametes, sperms, ova or eggs, fertilization, zygote and embryo which are involved in sexual reproduction.An animal having male sex cells called ‘sperms’ in its body is called male and an animal having female sex cells called ‘ova’ or ‘eggs’ in its body is called female.
Gametes: The cells involved in sexual reproduction or we can say that they are sexual reproductive cells. They are of two types: male gametes and female gametes. The male gamete in animal is called ‘sperm’ and the female gamete in animals is called ‘ovum’ or ‘egg’. Also female gamete or female sex cell is known by two names: ovum and egg both are same. The plural of ovum is ova. The ovum or egg contains water and stored food. Nucleus is the important part of ovum. Sperm cells are hundreds or thousands time smaller than ovum or egg and have a long tail. The sperm are motile which can move independently with the help of their tails.
Fertilization: The fusion of a male gamete with a female gamete to form a zygote during the sexual reproduction i.e. the fusion of a sperm with an ovum or egg to form zygote is called fertilization. The zygote is also known as ‘fertilized egg’ or ‘fertilized ovum’. This zygote grows and develops to form a new baby. The stage of development between the zygote or fertilized egg and the newly formed baby is called embryo.
Internal and external fertilization: The fertilization which occurs inside the female body is called internal fertilization i.e. it takes place in mammals including human beings, birds and reptiles. The fertilization which occurs outside the female body is called external fertilization i.e. it takes place in amphibians like frogs, toads and fishes.
The method in which a zygote grows and develops in to a full organism also varies in different animals. As in humans zygote grows and develops in to a baby inside female body and gives birth to a young ones, in animals like cats, dogs etc also gives birth to young ones but in birds it is entirely different which lay eggs. For example: Hen sits on its egg to give warmth so that zygote grows and develops to form a complete chick. This chick then comes out from egg by breaking its shell. So, all the organisms do not give birth to individuals like humans do.
It is important to understand that why the amount of DNA does not get doubled during sexual reproduction?
Gametes are also known as reproductive cells which contains only half the amount of DNA or half number of chromosomes as compared to the normal body cells of an organism. So, when male gamete combines with female gamete during sexual reproduction, then the new cell ‘zygote’ will have the normal amount of DNA. Human sperm has 23 chromosomes and human egg has also 23 chromosomes, after fusion 23 + 23 = 46 chromosomes, which is the normal number of chromosomes.
