LESSON 1: INTRODUCTION Flashcards
The greatest progressive minds of embryology
have not looked for hypotheses; they have
looked at embryos
Jane Oppenheimer (1955
Merging of two sciences (Embryology and
Genetics) that are intricately intertwined in the
development of the organisms.
Developmental Biology
Study of the origin and development of an
organism from a fertilized egg to the period
resembling an adult for
Embryology
Embryology is foundation of modern sciences like:
anatomy,
pathology,
genetics,
evolution,
histology,
immunology,
physiology,
cellular biology,
ecology
Embryology is a Mechanisms on the development of the organisms that is mainly responsible for the ___________ of animals.
great diversity
Deals with organogenesis and postnatal
development
Developmental Biology
organogenesis and postnatal development
includes:
neoplastic growth,
metamorphosis,
regeneration,
tissue repair
abnormal proliferation of cells (tumors)
Neoplastic Growth
the regrowth of body parts from pieces of
organism.
Regeneration
repair of tissue at levels of complexity ranging
from the molecular to the organismal level.
Tissue Repair
- Genetic mechanisms involved in the
development of an organism. - Manifestation of traits coded in the genes.
-Genotype translated into phenotype..
Developmental Genetics
two times bigger than ordinary baby zebra (foal)
Zebroid foal (Gene spliced zebra and donkey)
Fields of Embryology includes:
1.Descriptive Embryology
2.Comparative Embryology
3.Experimental Embryology
4.Chemical Embryology
5.Reproductive Biology
6.Reproductive Biology
7.Teratology
-Accounts on the processes of development which transformed a single cell zygote to a multicellular organism .
-Answers the question “what” .
-A step by step process
-Describes the new techniques of serial section and of making three-dimensional wax plate reconstructions
Descriptive Embryology
Analysis of similarities and differences in the development of different vertebrate groups
Provides insight that “ontogeny recapitulates phylogeny”
19th century
Provides valuable clues to taxonomic relationship among species by studying embryonic development
The driving force was the greatest interest in evolution, dominating factor in biology
Led to the recognition of different modes of development of many species and adoption of a number of species as model systems for experimental studies
Comparative Embryology
stage in which embryos of different groups are virtually alike.
Comparative Embryology: Stage 1
Testing a hypothesis and manipulating the embryo by experiments
Tissue and organ transplants – homotransplantation & xenotransplantation
Acquisition of detailed structural information on embryos
Seek to understand causative factors in the development by posing hypothesis and testing them by manipulating the embryos
Experimental Embryology
One of the pioneer of Experimental Embryology
Wilhelm Roux
Wilhelm Roux (1850 – 1924) is a pioneered in the field of experimental embryology ; his experiments provided proof for__________ or _________________
preformation or epigenesis doctrine
Roux coined the term _________________
“developmental mechanics”
Roux coined the term “developmental mechanics” ;____________ prefers “epigenetics” because development is brought about by a series of causal interaction between the various parts
Waddington
Arose from the rapid growth of research related to problems of conception and contraception
Problems of conception and contraception
Reproductive Biology
Reproductive Biology place a heavy emphasis on:
1.Normal gametogenesis
2.Transport of gametes and fertilization
3.Endocrinology of reproduction
4.Early embryonic development
5.Implantation of the mammalian embryo
Chemical and physical events in development
Interaction of factors affecting development
1930 – 1940
Provided descriptive information about chemical and physiological events in the embryo
Chemical Embryology
Middle Ages
Study of birth defects.
Deals with abnormalities and malformations in development due to genetic events and exogenous factors
Teratology
Genetic events that contributes to teratology
Mutations
Aneuploidy
Translocation
Exogenous factors that contributes to teratology
Drugs
Radiation
Alcohol
Bacteria and Viruses
A condition in which the long bones of the limbs are either absent or severely deficient.
Caused by genetic inheritance and/or mutations due to radiation and by oral intake of a drug named Thalidomide which was prescribed as mild sedative to pregnant women.
Phocomelia (Phoco – seal; Melia - limb like a seal’s flipper)
In contemporary society, _______________ and embryo transfer allowed childless couples to have children from their own genetic heritage (test tube baby)
in-vitro fertilization (IVF)
Problems with IVF and ET: Obtaining fertile eggs from mother by laparoscopy —> __________
problem of fertility drugs
Problems with IVF and ET: Surrogate mothers—>________
refusal to give up baby
Problems with IVF and ET: Manipulation of embryos—>
chimeras, cloning
Other Problems with IVF and ET
Frozen embryos
Gene transfer
Diagnosis of genetic diseases
Test-tube baby or In-vitro fertilization
Embryo transfer
Animal cloning
Embryology In Contemporary Society
Process of creating a genetically identical living being
Cloning
First ever cloned animal
Dolly the Sheep
Researchers from ___________ were the ones who successfully produced a clone from an adult somatic cell
Roslin Institute
Posed the question on how the different parts of embryo were formed.
defined preformation and epigenesis.
Aristotle (384 - 322 B.C.)
a miniature embryo already existed and got bigger
PREFORMATION
gradual formation of new structure (like knitting of net)
EPIGENESIS
Two Schools of Thought
Spermists and Ovists
the sperm contained the new individual in miniature and is merely nourished in the ovum
Spermists
Encasement Concept: “__________” – tiny human in the head of sperm
homunculus
argued that the ovum contained a minute body which was stimulated to grow by the seminal fluid.
Ovists
strengthened the ovists’ cause when he discovered that some of the eggs of insects can develop parthenogenetically
Charles Bonnet
Learned much about the structure of relatively advanced fetuses.
Restriction:The minute dimensions of early embryos prevented serious analysis.
Solution:The development of the microscope (17th century).
Galen (130-200 A.D.)
First to see human sperm cells with a crude microscope.
From a drop of pond water, he saw bacteria, protozoans and the sperm cells.
Anton Van Leeuwenhoek and Hamm (1677)
Founder of Modern Reproductive Biology
Described the ovarian follicles
First to describe the Fallopian tubes
Reiner De Graaf (1672)
What do you call the condition where in the embryo develop in the fallopian tube?
Ectopic Pregnancy
An Italian priest, physiologist, and natural scientist.
Demonstrated that in normal circumstances, both female and male sex products are necessary for the initiation of development.
Lazzaro Spallanzani (1729-1799)
Italian embryologist
Accurately described development of the chick in its egg.
Published the first microscopic account of chick development (1672).
Unconvinced of epigenesis because the unincubated egg had many structures.
Marcello Malpighi (17th Century)
Russian zoologist
Developed the science of comparative embryology
Existence of germ layers in embryos
nvestigated on cleavage.
Discovered the chick notochord and the mammalian egg.
Karl Ernst Von Baer (1792-1876)
VON BAER’S LAW (short)
“The more general basic features of any animal group appear earlier in development than do the special features that are peculiar to different members of the group.”
Karl Ernst Von Baer also proposed the _____________
GERM LAYER THEORY
GERM LAYER THEORY is the what?
development of ectoderm, mesoderm, and endoderm
Von Baer’s Law (elaborated)
1.The general features of a large group of animals appear earlier in development than do the specialized features of a smaller group
2.Demonstrated the existence of germ layers in embryos
With the formulation of the cell theory by Schleiden and Schwann, the foundation of modern embryology was laid down and embryology as a science began.
German biologist
Proposed that embryonic development occurs through progressive remodeling and growth.
Supported the theory of epigenesis
Caspar Friedrich Wolff (18th century)
The Cell Theory
- Cells are the basic unit of life
- Cells arose only from cells.
- Cells contain genetic information which is inherited by the offspring.
German biologists
Proposed the Cell Theory
Development must be via epigenesis
The foundation of modern embryology was laid down and embryology as a science began.
Matthias Schleiden and Theodore Schwann (1836-37)
German biologist
Observed sea urchin’s egg fertilization and cleavage
Distinguished between soma (body) and germ-cell line (gametes).
August Weissman (1880)
vehicle for protecting and perpetuating germ plasm
SOMATIC CELLS
important for perpetuation of the species; where offspring inherit their characteristics
GERM-CELLS
In each generation, germ cells give rise to both somatic and germ cells, but inheritance is through __________ only.
germ cells
During Inheritance, Changes that occur due to mutation in _________ can be passed on to their daughter cells but do not affect the germ-line
somatic cells
August Weissman: The zygote contains ______ derived from the egg and sperm.
two nuclei
August Weissman: Nuclei contain the factors that are ___________ distributed in the daughter cells
asymmetrically
August Weissman: The fate of each cell is predetermined in the egg by the factors it would receive during _______.
cleavage
August Weissman: The nuclei being asymmetrically distributed is a model called mosaic since the egg is considered a ___________________
mosaic of discrete localized determinants
Major phases of the life cycle of a typical vertebrate (Reproductive life cycle)
ADULT—> gametogenesis —> egg + sperm—>Fertilization—> cleavage—> gastrulation—> organogenesis —> fetal growth—> hatching or birth—> juvenile —>repeat the process
Post reproductive Period
Adult—> senescence—> death
German zoologist
Developed the controversial Recapitulation Theory/ Biogenetic Law - “ontogeny recapitulates phylogeny“.
Claiming that an individual organism’s biological development, or ontogeny, parallels and summarizes its species’ entire evolutionary development, or phylogeny.
Ernst Haeckel (1868)
German biologist
Demonstrated that it was possible to remove large pieces from eggs, such as shuffling the blastomeres at will or taking some away and thus interfere in many ways, yet not affect the resulting embryo
Any single monad in the original egg cell was capable of forming any part of the completed embryo
Leads to the terms totipotent cell (total + potential) and pluripotent cell
Hans Adolf Eduard Driesch (1867-1941)
can generate all cells in an organism.
Totipotent cell
can generate certain cells in an organism
Pluripotent cell
ability of embryo to develop normally even if some cells are removed or rearranged
Regulative Development
The outcome of Driesch’s experiment on sea urchin embryo’s which first demonstrated the phenomenon of regulation.
After separation of cells at the two-cell stage, the remaining cell developed a small, but whole, normal larva which contradicts Roux’s earlier finding that if one of the cells of a two-cell form an embryo is damaged, the remaining cell develops into a half embryo
- a partial second embryo can be induced by grafting a small region of a new embryo onto a new site on another embryo.
- grafted tissue was taken from the dorsal lip of the blastopore which was called organizer or evocator – responsible for controlling the organization of a complete embryonic body
Transplantation Experiment
Who conducted or defined the transplantation Experiment
Hans Spemann & Hilde Mangold (1924)
Danish biologist
Distinguished between genotype and phenotype
Wilhelm Johannsen (1857-1957)
genetic information or endowment of an organism acquired from its parents
Genotype
visible appearance, internal structure or biochemistry at any stage of development
Phenotype
Relationship between genotype and phenotype
How the genetic endowment (genotype) is “translated/expressed (phenotype)” during development to give rise to a functioning organism
German embryologist
Explained the Ablation Experiment or Embryonic Extirpation
Development of frog is based on Mosaic mechanism.
Wilhelm Roux (Late 1896)
Ablation Experiment or Embryonic Extirpation:
Roux Took 2- and 4- cell frog embryos and destroyed some of the cells of each embryo with a hot needle to determine whether the remaining cell will give rise to only half an embryo or could restore the deficiency during subsequent development
worked on mutant genes of mouse and Drosophila
integrated genetics and embryology = Developmental Genetics
Defined epigenetics
Gluecksohn and Waddington (1930)
determine the properties of a cell during development
Genes encode proteins
- development is brought about by a series of causal interactions between the various parts.
-reminds one that genetic factors are among the most important determinants of development.
EPIGENETICS