1. Introduction to Embryology
Definition of Embryology:
It is the study of the growth and differentiation undergone by an organism in the course of development from a single fertilized egg cell into a highly complex and independent living being like parents.

2. Introduction to Embryology
Importance/Branches of Embryology:
Descriptive embryology: Deals with the description of the structural feature of embryos of various ages.
Comparative embryology: Comparative study of the structural features among the embryos of different animals.
Experimental embryology: Important in the field of genetics, cloning of animals and test tube baby.
Chemical embryology: Studies regarding chemical components of the embryo, e.g. DNA.
Teratology: Studies of the malformation of the embryo.

3. Introduction to embryology
Objectives of embryology:
Gain the knowledge of evolution.
Know the teratological defects of the fetus.
Application of embryological knowledge towards pathology, immunology and other applied subjects.
By applying the knowledge we can increase the conception rate of animals.
Commercial purpose- cloning of animals and its marketing.

4. Introduction to embryology
Methods of study:
Dissection: Gross dissection of embryos at different stage.
Microscopic sections: By serial section with the help of microtome.
Descriptive study: Detail study.
Experimental study: By various drugs/chemicls/or by physical means.

5. Introduction to embryology
Factors controlling growth of the embryo:
Temperature.
Nutritional factor.
Hormone, e.g. thyroxin
Vitamins, e.g.
Vitamin A is needed fro the weight gain of the embryo, Vitamin B2, C, and D is essential for the growth of the embryo.
5. Minerals: Ca, P are necessary for the development of the bones.
Embryo needs other vitamins and minerals like adult for its development.

6. Mitosis
Mitosis is a process whereby a cell devides its chromosomes complement evenly between its daughter cells. Mitosis can be subdevided into four phases: Prophase: Chromosomes coil, contract, condense and thicken at this stage. Metaphase: Mitotic spindle is formed by microtubules and centrioles. Chromosomes appear at the equatorial position of the cell. Anaphase: The V-shaped chromosomes move towards the two pole of cell. Telophese: A cell devides into two daughter cell.

7. Mitosis during Spermatogenesis and Oogenesis
During Spermatogenesis Spermatogonia undergoes several mitotic divisions and some of the spermatogonia differentiated into Primary Spermatocytes.
During Oogenesis Oogonia undergoes several mitotic divisions and some of them differentiate into Primary Oocytes.

8. Number of Chromosomes in Animals Including Man
Man pairs
Dog and Hen pairs
Horse pairs
Cattle and Goat pairs
Sheep pairs
Monkey pairs
Pig and cat pairs
Pigeon pairs

9. Spermatogenesis and Chromosomes
Cell type Ploidy/chromosomes DNA copy/Chromatids Process
Spermatogonium Diploid (2N) / C / Spermatocytogenesis
(Mitosis)
Pri. Spermatocyte Diploid (2N) / C / Spermatidogenesis
(Meiosis 1)
Sec. Spermatocytes Haploid (N) / C / Spermatidogenesis
(Two) (Meiosis 2)
Four Spermatids Haploid (N) / C / Spermiogenesis
Four functional Haploid (N)/ C/ Spermiation
Spermatozoa

10. Oogenesis and Chromosomes
Cell type ploidy Process Process completion Oogonium diploid Oocytogenesis 3rd trimester (Mitosis) (Forming Oocytes) Primary diploid Ootidogenesis Dictyate in prophase I Oocyte (meiosis 1) for up to 50 years Secondary haploid Ootidogenesis Halted in metaphase II (meiosis 2) until fertilization Ovum haploid ** Dictytate: Prolonged resting phase in oogenesis.

11. Steps of OOgenesis
Meiosis I
Meiosis II

12. Polar Body Primary oocyte Dictyate until puberty of animals
1st Meiotic division in the ovary.
The primary oocyte in the Graafian follicles completes the
First meiotic division to become
a secondary oocyte.
During this first meiotic division chromosome pairs are established and mixture of parental genetic material established.
The first meiotic division complete before ovulation.
Ovum
2nd Meiotic division in
The fallopian tube
Before or after fertilization
Depend on the species of animals.
Secondary oocyte