Introduction to Embryology Definition of Embryology It is

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.

Introduction to Embryology Importance/Branches of Embryology: 1. Descriptive embryology: Deals with the description of the structural feature of embryos of various ages. 2. Comparative embryology: Comparative study of the structural features among the embryos of different animals. 3. Experimental embryology: Important in the field of genetics, cloning of animals and test tube baby. 4. Chemical embryology: Studies regarding chemical components of the embryo, e. g. DNA. 5. Teratology: Studies of the malformation of the embryo.

Introduction to embryology Objectives of embryology: 1. Gain the knowledge of evolution. 2. Know the teratological defects of the fetus. 3. Application of embryological knowledge towards pathology, immunology and other applied subjects. 4. By applying the knowledge we can increase the conception rate of animals. 5. Commercial purpose- cloning of animals and its marketing.

Introduction to embryology Methods of study: 1. Dissection: Gross dissection of embryos at different stage. 2. Microscopic sections: By serial section with the help of microtome. 3. Descriptive study: Detail study. 4. Experimental study: By various drugs/chemicls/or by physical means.

Introduction to embryology Factors controlling growth of the embryo: 1. Temperature. 2. Nutritional factor. 3. Hormone, e. g. thyroxin 4. Vitamins, e. g. Vitamin A is needed fro the weight gain of the embryo, Vitamin B 2, 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.

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.

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.

Number of Chromosomes in Animals Including Man • • Man Dog and Hen Horse Cattle and Goat Sheep Monkey Pig and cat Pigeon 23 pairs 39 pairs 32 pairs 30 pairs 27 pairs 21 pairs 19 pairs 8 pairs

Spermatogenesis and Chromosomes Cell type Ploidy/chromosomes Spermatogonium DNA copy/Chromatids Diploid (2 N) / 46 2 C / 46 Pri. Spermatocyte Diploid (2 N) / 46 2 C / 46 Sec. Spermatocytes Haploid (N) / 23 (Two) Four Spermatids Haploid (N) / 23 2 C / 46 Four functional Spermatozoa Haploid (N)/23 1 C / 23 1 C/23 Process Spermatocytogenesis (Mitosis) Spermatidogenesis (Meiosis 1) Spermatidogenesis (Meiosis 2) Spermiogenesis Spermiation

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

Steps of OOgenesis Meiosis II

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