The document provides an introduction and historical overview of principles of experimental embryology. It discusses early embryological observations by Aristotle and others. Key experiments by Roux, Driesch, Hertwig, and Boveri helped establish that the fertilized egg contains all the genetic information to develop into a complete organism. Later, Morgan, Warburg, Just, Hamburger, Harrison, Spemann, and others further advanced the field through studies of cell differentiation, gene expression, oxygen consumption, and tissue transplantation in various model organisms. Pioneering work by Brachet, Briggs and King also helped establish the roles of DNA, RNA, and nuclear transfer in development.

1. ‫الرحيم‬‫الرحمن‬‫هللا‬‫بسم‬
‫مبادئ‬
‫يبي‬‫ر‬‫التج‬‫جنة‬
‫أ‬
‫ال‬‫علم‬
Zoo. (424)
Principle of Experimental
Embryology 2(1+1)
‫تاريخية‬ ‫ولمحة‬ ‫مقدمة‬
Introduction and Historical review

2. Principal of Experimental Embryology :Zoo/424
Introduction and historical review
• The embryology science reported by some verses of
the Quran in particular with regard to human creation
"so let man see, create, creation of water flush from between
back bone and ribs,(altraeb).... ،‫خلق‬ ‫مما‬ ‫اإلنسان‬ ‫فلينظر‬
‫خلق‬
‫ماء‬ ‫من‬
‫الصلب‬ ‫بين‬ ‫من‬ ‫يخرج‬ ‫دافق‬
‫والترائب‬ " Yes it is God sinah in this
life,
• All multicellular organisms arose from the mating
between male and female gametes (fertilization)
• Note the embryos in different developmental stages
from gamete to cleavage (from Zygote to blastula
stage).
• Then Gastrulation stage, the formation of the three
different embryonic layers, ectoderm,mesoderm and
endoderm(gastrula).
• Later the organogensis stage: from these 3
embryonic layers were all the organs of the embryo
will form.
• Finally the grow and increase in size until the exit of

3. Introduction :
The development of multicellular organisms from a
single cell—the fertilized egg—is a brilliant thinking .
During embryonic development, the egg divides to
give rise to many millions of cells ,which form structures
as complex and varied as eyes, arms, heart, and brain.
This amazing achievement raises many questions.
-How do the cells arising from division of the fertilized
egg become different from each other?
-How do they become organized into structures such as
limbs and brains?
What controls the behavior of individual cells so that
such highly organized patterns emerge? -How are the
organizing principles of development embedded within the
egg, and in particular within the genetic material, DNA?

4. - What controls the behavior of individual cells so that such
highly organized patterns emerge? -How are the organizing
principles of development embedded within the egg, and in
particular within the genetic material, DNA?
-Much of the excitement in developmental biology today
comes from our growing understanding of how genes direct
these developmental processes, and genetic control is one of
the main themes of this course.
-Several of factors are involved in controlling
development, but we will focus only on those that have key
roles and illustrate general principles.
-The development of an embryo from the fertilized egg is
known as embryogenesis. One of its first tasks is to lay down
the overall body plan of the organism, and we shall see that
different organisms solve this fundamental problem in several
ways.

5. Branches of Embryology
Embryology has many sub-branches in it. They are:-
• 1- Descriptive Embryology
• It is applied to the method of study concerned with the direct
observation and description of embryological development.
Embryology in ancient times started as a branch of study
based on the direct observation and description by scientists
like Aristotle (340 B.C.), Fabricius (1537 – 1619), Harvery
(1578 – 1657) and so on.
• 2- Comparative embryology
• It is the embryological development of different animals and
studied and compared. Comparative embryology throws
much light on the understanding of evolution and
phylogenetic significance. It also give some ideas on the
developmental stages of certain animals in whose case the
study of development is different.

6. • 3- Experimental Embryology
• In it is experiments are used for studying the
developmental stages. It helps to understand the
fundamental developmental mechanisms. In
experimental embryology the various parts of
developing embryo are removed, transplanted,
parts exchanged or the environmental conditions
altered. This helps to understand induction,
gradient system, etc. Experimental embryology
is also called casual embryology of analytical
embryology. Roux (1850 – 1924) is the pioneer
in the field of experimental embryology.

7. 4- Chemical Embryology
The developmental stages are studied by biochemical
and physiological techniques. It is also called
physiological or biochemical embryology. Needham
(1931) is the pioneer in this field.
5- Teratology
It is a branch of embryology concerned with the study
of malformations or abnormal development.
6- Developmental Biology
It includes not only embryonic development but also
postnatal processes such as normal and neoplastic
growth, metamorphosis, regeneration and tissue
repair in both animal and plant .

8. Historical and background of Exp. Embryology
Aristotle (384 – 322 B.C ):
Before the 17th century embryological knowledge was
based on the writings of Aristotle and Galen. Embryology
as a branch of biology was initiated by the famous Greek
philosopher Aristotle (384 – 322 B.C.).
He was the first embryologist to describe the development
and reproduction of many kinds of organisms in his book
entitled "Degeneratione Animalium". He believed firmly
that the complex adult organism develops from a simple
formless beginning.

9. Historical and background of Exp. Embryology
cont. Aristotle (384 – 322 B.C ):
Thus he laid the foundation for the basic principles of
epigenesist, a theory postulated after 2000 years. For this
Aristotle is honored as the father of embryology. Aristotle
has written that the male contributes the semen and the
female contributes the contamenia. The semen is secreted
by testis and it is hot and active. The catamenia is carried
through very fine vessels into the uterus. It is equivalent to
the menstrual blood. He had no knowledge of ovary. He
thought that the female reproductive system is formed of
uterus only and not of anything else.

10. Cont .Historical and background of Embryology
Wilhelm Roux (1888)and Hans Driesch
(1892) both In separate experiments,
Wilhelm Roux (1888) and Hans Driesch
(1892) set out to determine whether
epigenesis or preformation was correct.
Both allowed a fertilized egg to divide to the
two-cell stage. Roux, using amphibian
embryos (frogs, toads, salamanders), killed
one of the two cells with a hot needle.
Driesch, using echinoderm embryos (sea
stars, sea urchins, sea cucumbers),
completely separated the divided cells.

11. Cont .Historical and background of Embryology
Wilhelm Roux (1888)and Hans Driesch (1892)
An entire animal developing from a
single cell would support epigenesis.
A portion of the animal developing
would favor preformation. What was
the result? Interestingly, Roux
described the formation of a half
embryo that he called a “hemiembryo”
(figure a), and Driesch found that each
cell retained the potential to develop
into an entire organism (figure
b).

12. August Weismann 1880s
Propose that the germ plasma theory: The egg
and sperm contribute chromosomes equally to
the zygote (fertilized egg). The chromosomes
are carriers of the hereditary potentials, and the
germ cells (gametes) of the embryo are the only
ones to carry the complete set of hereditary
potentials (nuclear determinants), whereas each
somatic (body) cell type contains only part of
these potentials required for the specific cell
type.

13. • Oscar Hertwig (1872)
• He repeat the Wilhelm's experiments, but he
separate the 2 cell frog embryo from them and
improved that each cell had a potential to grow, but
the embryo result is half size than normal embryo.
This experiment is considered the one of
explanations of twins formation result from one egg.
• Theodor Boveri (1902)
• He studied the effect of nucleus and cytoplasm on
the development of the sea urchin fertilized ovum by
study of controls and filaments formation during
different division stages. Also, he tries to
insemination of specific species ovum with another
species sperm, and he found that the chromosomes
are different in quantity and numerically.

14. Thomas Hunt Morgan (1866 – 1945)
• He is the first scientist that suggested that the
embryonic development is controlled by expressions
of different genes, and he awarded Nobel prize for
discovered the mutations in Drosophila and their
role in understand the role of genes in heredity.
• Otto Warburg (1908 – 1910)
• He studied the respiratory mechanism in sea urchin
embryo cells, and he considers the first scientist
who definition oxygen consumes in respiratory of
ovum and embryonic cells. Their study resulted in
know that the fertilization make to increase the
cellular reparatory rate of fertilized ovum. So, he
discovered the cytochrome Oxidase and he
awarded the Nobel prize on this discovery at 1931.

15. Ernest E. Just (1883 – 1941)
• He descriptive the changes occurred around the oocytes during
the fertilization in sea urchin and he studied the
parthenogenesis to understand the relationship between
penetrate of sperm and the first division of Nematoda oocytes.
• Viktor Hamburger (1954)
• The discovery of chick embryo's neural sector. Hamburger
proposed an antiapoptotic action of the hypothetical target-
derived trophic signals, identified as nerve growth-stimulating
factor, later named nerve growth factor (NGF).
• Ross Granville Harrison (1870 – 1975)
• He successfully cultured frog neuroblasts in a lymph medium
and thereby took the first step toward current research on
precursor and stem cells. He was considered for a Nobel prize
for his work on nerve-cell outgrowth, which helped form the
modern functional understanding of the nervous system, and he
contributed to surgical tissue transplant technique.

16. • Hans Spemann and Mangold (1924)
• Hilde Mangold’s experiment involved taking a piece of
the lip of the blastopore of the gastrula stage of the
amphibian embryo and grafting it to the wall (flank) of
another gastrula at a site distant from the host
blastopore, and thereby induced a secondary axis of
polarity in the host that eventually developed into a
secondary embryo.
• In 1935 Spemann received the Nobel Prize for
Medicine or Physiology as the first embryologist.

17. • Jean Brachet (1988 – 1909)
• In 1933 Brachet was able to show that DNA was found in
chromosomes and that RNA was present in the cytoplasm of all
cells. His work showed that RNA plays an active role in protein
synthesis. Brachet also carried out pioneering work in the field
of cell differentiation. Brachet later demonstrated papers that
differentiation is preceded by the formation of new ribosomes
and accompanied by the release from the nucleus of a wave of
new messenger RNA.
• Robert Briggs (1983 – 1911) and Thomas Joseph King
• He was a scientist who in 1952, together with Thomas Joseph
King, cloned a frog by nuclear transfer of embryonic cells.
• The same technique, using somatic cells, was later used to
create Dolly the Sheep by Willmut and Kith Kamble 1997 .
Their experiment was the first successful nuclear
transplantation performed in metazoans (mammles).