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 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.
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.
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 (2N) / 46
2C / 46
Pri. Spermatocyte Diploid (2N) / 46
2C / 46
Sec. Spermatocytes Haploid (N) / 23
(Two)
Four Spermatids
Haploid (N) / 23
2C / 46
Four functional
Spermatozoa
Haploid (N)/23
1C / 23
1C/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
Process completion
Oocytogenesis
3rd 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 I
Meiosis II
Polar Body
Primary
oocyte
Dictyate until puberty of animals
 1st Meiotic division in the
Ovum
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
2nd Meiotic division in Secondary oocytecomplete before ovulation.
The fallopian tube
Before or after fertilization
Depend on the species of animals.