Topic 1-4

• Descriptive Embryology

  ●         Started as an old science, one of the first

  ●         Dawn of biology in ancient Greece
• Aristotle (384-322 BC)

  ●         First to study embryos focused on chick

  ●         Wrote first textbooks in zoology and treatises on reproduction and development
• Spontaneous generation - scientific theory by Aristotle that states living organisms arise from nonliving matter and that such processes were regular.
• Hermaphroditism - condition where a living organism has both male and female reproductive parts
• Bisexual reproduction - believed that the semen provides the force towards development and the menstrual blood provided the matter
• Modeling principle of any organism is “energia” or “entelecheia”, the principle bearing its goal and end in itself. The ultimate energy is called its psyche or soul
• 3 types of soul operating in the organism

  1. vegetative
  2. animal: when they start to move
  3. spiritual: when they have consciousness
• RENAISSANCE OF DEVBIO

  • ovaries and testes, eggs and semen then eventually sperm were studies
  • advent of microscope
• RENAISSANCE OF DEVBIO

  William Harvey (1578-1657)

  • proposed that organisms, but not all, come from egg
  • Omne vivum ex ovum
  • Exercitationes de Generatione Animalium
• RENIASSANCE OF DEVBIO

  Spermists - claim that the embryo comes from one sperm only; disputed by physics
• RENIASSANCE OF DEVBIO

  Ovissts - all generations will come from an egg only; disputed by physics
• RENIASSANCE OF DEVBIO

  Preformationism - ovists and spermists theory
• RENIASSANCE OF DEVBIO

  Leeuwenhoek (1632 - 1723) and Hartsoeker - so-inventors of the microscope claimed to have seen little men inside individual spermatozoa
• RENIASSANCE OF DEVBIO

  Van Leeuwenhoek A. - spermatic animalcules

  
• RENAISSANCE OF DEVBIO

  Dalenpatius - Homunculi in the human male semen

  
• RENAISSANCE OF DEVBIO

  Needham - Preformation according to the ovist theory

  
• Hartsoeker N. - human spermatozoan with homunculus

  
• RENAISSANCE OF DEVBIO

  Emboitement Theory - physics; hindi pwede na one sperm will hold all future gen

  • The emboîtement theory proposed that all living beings were created at the same time, and each female carried within her all future generations in a miniature form.
• Fertilization Discovered

  Lazaro Spallanzani (1729-1799) - first to observe that female egg develops only in the presence of male semen but believed that spermatozoa were parasites
• Fertilization Discovered

  Oscar Hertwig (1875) - both sperm and egg contribute to form an embryo
• Preformation vs. Epigenesis

  Epigenesist - embryo forms gradually out of formless materials in the yolk (Caspar Friedrich Wolf (1738-1794))
• Preformation vs. Epigenesis

  Vitalism - vital force to life is the prime mover for such grand unfolding of the organism
• COMPARATIVE EMBRYOLOGY

  Karl Ernst von Baer (1792-1876)

  • another vitalist
  • discovered eggs in many mammalian species
  • preformed comparative studies
• COMPARATIVE EMBRYOLOGY

  Ernst Haeckl (1834-1919)

  • built on Baer's study and proposed the controversial biogenetic law which gave scientific basis for racial discrimination of the Third Reich
  • bastardized von Baer
• COMPARATIVE EMBRYOLOGY

  Embryo Resemblances: von Baer

  • stage where one would look very alike from the other (even if it comes from diff eggs)
  • all vertebrates pass through same stages and possess similar structures that will later on differentiate into different structures and appendages
  • pass through similar stages that will later on differentiate them from each other
• COMPARATIVE EMBRYOLOGY

  >>> vs. Haeckl

  • every stage of the development of organisms is final
  • --- Lower forms: every stage is final (single stage)
  • --- Higher forms: ontogeny recapitulated phylogeny
  • every organism has a hierarchy: there are higher forms and lower forms
  • there are lowly forms of human beings and cultures
  • there are super races and primitive races
• ERA OF EXPERIMENTAL EMBRYOLOGY

  E.B. Wilson

  • leading cytologist at the turn of the century
  • recognized that embryonic development is a manifestation of changes in the cell
• ERA OF EXPERIMENTAL EMBRYOLOGY

  T.H. Morgan and Wilson

  • lively debate on whether the determinants of development came from the nucleus or cytoplasm
  • (Morgan: cytoplasm, Father of Modern Genetics)
  • its the DNA that is unique in the nucleus
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  August Weismann (1834-1914)

  • germ plasm theory
  • zygote: during division; each cell got different proportions
  • blind
  • multicellular organisms consist of germ cells that contain and transmit heritable information, and somatic cells which carry out ordinary bodily functions.
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  Wilhelm Roux

  • very first to manipulate zygotes or oocytes
  • Father of Experimental Dev Bio
  • exp on frog eggs (1888)
  • fertilized eggs on 1st cleavage -> 2 cells -> killed on of cells -> to prove what happens to the dead and living cell -> living cell: continued to divide -> alive: half embryo -> died
  • tama daw ang preformationism: kalahati lang kc ang nabuhay

  
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  Hans Driesch

  • perfected ROux's exp
  • tinusok tapos pinaghiwalay; ung buhay part nabuhay to develop into a whole embryo
  • experimented on sea urchin eggs (1876-1941)
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  Theodore Boveri and Sutton (1902)

  • chromosome thoery
  • genes
  • different labs
  • Boveri - Europe; Sutton - US
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  Gregor Mendel

  • rediscovered paper
  • hereditary traits come from things from the mother and the father
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  Wilson's Advocacy

  • Nucleus is the source of determinants that guide morphogenesis and differentiation of blastomeres in embryo
  • believed in the studies of Boveri and Sutton
• ERA OF EXPERIMENTAL EMBRYOLOGY

  Studies fueling the debate

  Side of TH Morgan

  • Morgan: believed that the cytoplasm was the source of determinants causing differentiation of the cells and guiding morphogenesis
  • exp on ctenophore seemed to prove him correct
  • Works of Nettie Stevens: proved him wrong; this caused him to champion the nucleus and chromosomes as guides of morphogenesis
  • Established presence of sex chromosomes on nucleus
• ERA OF EXPERIMENATAL EMBRYOLOGY

  Studies of Genetics was Born from this Conflict

  • those who believed in chromosomes as morphogenetic guide separated from those who believed in cytoplasm; they established genetics as a science
  • they concentrated on chromosomes and genes to explain all aspects of development
  • but many issues were unresolved
• Unresolved Issues

  • How exactly do genes determine hereditary trait?
  • How does the nucleus regulate metabolism?
  • How do the chromosomes which were identical in every cell of the organism direct different and changing types of cytoplasm?
  • Geneticists must provide evidence that genes control early stages of dev of structures not the terminal stages
  • What about the phenomenon of sex determination were environment determines sexual phenotype?
• BIRTH OF MODERN GENETICS

  • these unanswered questions caused a deep divide and caused “genes people” to form their own society, journal, lingo
  • they started an era of modern day genetics
• BIRTH OF MODERN GENETICS

  The Embryologist's Concerns

  • the die hard embryologist turned to study cellular and tissue interactions leading to the discovery of...
• BIRTH OF MODERN GENETICS

  ...discovery of:

  Hilde Mangold and Hans Spemann

  • discovered the primary organizer
  • dorsal lip: organizes 2nd set of cells??
  • Spemann: got Nobel Prize, Mangold did not because she was only a student