Growth and Development in Animal

Growth and Development in Animal
Animals begin their lives as single diploid cell called Zygote formed by the fusion of sperm and ova. Development of zygote into adult involves a series of stages, which may varies in different animals however the main stages are basically similar in all. A broad outline of early stages of an animals embryonic life can be represented as
1. Gametogenesis
2. Fertilization
3. Cleavage
4. Gasrulation
5. Organogenesis
6. Growth
1. Gametogenesis
The process of gamete formation is called gametogenesis. Ova and sperm are formed in Gametogenesis.
2. Fertilization
Ova and sperm are fuse together to form a diploid nucleus is called Fertilization.
3. Cleavage
Series of mitotic cell division to produce blastomeres is called Cleavage.
4. Gastrulation
Arrangement of cells into three germinal layers is called Gastrulation.
5. Organogenesis
The process in which body organs are form, cell interact and differentiate is called Organogenesis.
6. Growth
Increase in the size of organs to attain maturity is called Growth.
Development of Chick
The study of development of chick provides a basis for understanding the early differentiation of the organ system and the fundamental process of body formation, which is common to all vertebrates.
Structure of Egg
The structure of hen’s egg are as follows
Polylecithal Type
The egg of a hen is polylecithal type. In this egg, enormous amount of yolk is present which is used as energy during the process of development.
Primary Oocyte
When the egg is covered by a thin membrane called Vitelline membrane.
Animal Pole
Its upper part is called animal pole.
Blastodisc
The protoplasm is restricted to a very small area called Blastodisc or Germinal disc.
Secondary Oocyte
Primary oocyte become mature after releasing from the ovary is called Secondary Oocyte.