vittelogenesis.pptx

Vittelogenesis is a word developed from Latin vitellus-yolk, and genero-produce
Vitellogenesis (also known as yolk deposition) is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction of lecithotrophic organisms. In insects, it starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein. 
Yolks is the most usual form of food storage in the egg.
Yolks appear in the oocyte in the secondary period of their growth called vittelogenesis.
Thus,the formation and deposition of yolks is known as vittelogenesis
Characteristic
Yolks is a complex variable assembled component.
The principle component are protein,phospholipid and fats in different combination.
Depending upon these component yolks is distinguished into protein yolks and fatty acid
For eg- the avian contain 48.19% water , 16.6 % protein, 32.6% phospholipids and fats and 1% carbohydrates.

1. Development Biology Vittelogenesis By Miss Iram

2. Definition of vittelogenesis from  Latin   vitellus - yolk, and  genero - produce Vitellogenesis  (also known as  yolk deposition ) is the process of yolk formation via nutrients being deposited in the  oocyte , or female  germ cell  involved in  reproduction  of  lecithotrophic  organisms. In insects, it starts when the  fat body  stimulates the release of juvenile  hormones  and produces  vitellogenin  protein. 

3. Characteristic Yolks is the most usual form of food storage in the egg. Yolks appear in the oocyte in the secondary period of their growth called vittelogenesis. Thus,the formation and deposition of yolks is known as vittelogenesis Yolks is a complex variable assembled component. The principle component are protein,phospholipid and fats in different combination. Depending upon these component yolks is distinguished into protein yolks and fatty acid For eg- the avian contain 48.19% water , 16.6 % protein, 32.6% phospholipids and fats and 1% carbohydrates

4. Types of yolk In animals, the yolk is of 3 types 1. Granular yolk 2. Yolk platelets 3. Yolk sphere

5. Granular yolk It is the characteristic feature of invertebrates and lower chordates likes amphooxus and tunicates. The protein yolk is composed of fine granules which is evenly distributed into the cytoplasm of oocyte Yolk Platelets. It is found in most of vertebrates like cyclostomes, lung fishes, amphibians, reptiles and birds The yolk occur in the form of large granules Known as yolk platelets. The yolk platelets are oval and flattened in one plane.

6. The yolk Platelets contain 2 main proteinaceous substances . 1. Phosphovitin - it is highly phosphorylated protein Its molecular weight is 35000 D , 8.5% of phosphorus content is present 2. Lipovittelin- it is a protein major bound to lipid . Its molecular weight is 4000D . 17.5% of lipid content is present. In yolk Platelets, 2 molecules of phosphoviti are associated with one molecule of lipovittelin a structural unit The units are being arranged in Platelets in a crystalline lattice with a regular hexagonal packing. The yolk Platelets of bony fish have fat droplets inside its mass.

7. Yolk sphere The yolk of birds, reptile and bony fishes lies in a compact mass in the interior of a egg. The cytoplasm is restricted to their layer on the surface of the egg.

8. Function It store food in the egg. It influence the differentiation of neoplasm pattern of cleavage. The size of egg is determined by amount if yolk present in it. It is responsible for morphogenetic movement of elastomer during gastrulation. The mature of development of an organism is governed by amount of yolk present in the egg