|
||||||||
| Sample Notes Aadhar Institute is providing notes for M.Sc Biotech entrance, NET Life Science, GATE Life Science for studying in detail purchase our correspondence course. ANIMAL DEVELOPMENTAL BIOLOGY (EMBRYOLOGY) Development has 2 meanings :- The study of the developmental processes of the organism itself is termed as Ontogenic development. And to study the development of the organism if we study historical evolution. it is termed as Phylogenetic development. - . HISTORY : - (1) Aristotle is known as "Father of Embryology" He first studied the development in chick and other embryos. He gave its description in his book "Historia Animalia". (2) Leeuwenhock (1671) - He observed and described human sperm for the first time. - According to Hartsocker and Leeuwenhock there is present a small model of developing animal in the head of the sperm of that animal. This small model is called Homunculus. Both the scientists are called spermists, and this theory is called "Theory of spermist". (3) Swammer Dame, Haller, Bonette & Malpighi :- According to there scientists, small model of animal is present in the egg. These scientists are called, Ovists, and their theory is known as 'Ovists theory' (4) Schleiden & Schwann :- Both the scientists established the cellular structure of egg and sperm. (5) Pander :- He described the presence of three germinal layers in chick embryo. Fredrick wolf :- He first presented the "theory of Epigenesis". (6) Galtsaf & Waltan :- For the first time they gave the details of fertilization and embryo development. (7) Mullar :- He gave the Recapitulation theory. (8) Hackel :- he gave the details of Recapitulation theory and named it as the Bio-genetic law. - Bio-genetic Law :- According to it, each organism during its embryonal development, passes through all stages, through which, its species has evolved or embryo repeats its ancestry, i.e. Ontogeny recapitulates its Phylogeny. (10) "Carl Ernest Von Baer" :- He is known as the "Father of Modern Embryology." He gave the Baer's Law which in turn proves the Recapitulation theory. According to this law, during embryonal development, development of general structures takes place earlier and specific structures develop at last or later on. (11) A. Weisman :- He gave the theory of Germplasm or the theory of continuity of Germplasm According to him, there are 2 types of protoplasm in the body of animals :- (i) Somatoplasm (ii) Germplasm. According to him, Somatoplasm dies but the Germplasm is not destroyed, rather it is transferred to the progenies. (12) Wilhelm :- He studied embryonal development in frog and gave the Mosaic theory. He said that there occurs some Presumptive areas in the eggs of frog. These areas form specific structures during embryonal development. This is termed as "Promorphology". and these type of eggs are termed as the Mosaic eggs. (13) Hans driesch :- He studied embryonal development in sea-urchin and gave the Regulative theory. In the eggs of Sea-Urchin presumptive areas are not found i.e. Promorphology is not found. So, each part of the egg is capable of forming the complete embryo. These type of eggs are termed as Regulative eggs. purchase our correspondence course for images and diagrams (14) Boveri & Child --> He gave the Gradient theory to explain the Mosaic development in eggs, -> Acc to them, a metabolic gradient is present inside the eggs. -> Different parts of the egg have different metabolic rates. -> The rate of metabolism is faster at the animal- pole of the egg and is slower at the vegetal pole of the egg, -> Because of the different metabolic rates different structures form different parts of the egg. (15) Spemann:- He gave the "Theory of Organizers".According to it embryo has some special type of tissues, which induce development of some specific structures. These are termed as the organizers. These organizers secrete some special chemicals called Evocators which induce the formation of specific structures.He studied the embryo of frog and then concluded that ; in the gastrula stage of embryonal development in frog the dorsal lip of the Blastopore acts as an organizer for the formation of Head structures. If it is removed, then formation of head is stopped. Spemann got the Nobel prize for his theory of Organizers. (16) R.V. Graaf :-He studied a follicle in human ovary termed as "Graffian follicle". Gametogenesis :- . The process of formation and development of these gametes is termed as Gametogenesis", -> As a result of this process, male gamete sperm and female gamete egg is formed. -> The process of Gametogenesis is stimulated by the FSH or Follicle Stimulating Hormone and for this process Vitamin "A" and "E" are also necessary. -> The process of Gametogenesis has been divided into 3 substages :- (i) Multiplication phase. (ii) Growth phase. (iii) Maturation phase. |
||||||||
| ||Go to Home|| | >>Next Page | |||||||
|
||||||||
