Introduction to Genetics

• Jan Swammerdam proposed the Theory of Preformation

  17th to 18th century
• Atomic theory

  • All matter is composed of small invisible units called atoms
• Aristotle's belief about male semen


  It has the capacity to produce offspring of the same "form" as the parent
• Theory of Epigenesis


  • The organism is derived from a substance in the egg, which differentiates into adult structures during embryonic development
  • New structures, such as body organs, are not present initially but instead are formed de novo in the embryo
• Aristotle's belief about male semen


  It is generated offspring by cooking and shaping the menstrual blood produced by the female, which was the "physical substance" giving rise to offspring
• John Dalton proposed the Atomic theory


  1808
• Aristotle believed that male semen was formed from blood rather than from each organ
• William Harvey, an English anatomist, proposed the Theory of Epigenesis


  1600
• Cell theory

  • All organisms are composed of basic visible units called cells, which are derived from similar
• Embryo development according to Aristotle


  Embryo developed from the initial "setting of the menstrual blood by the semen into a mature offspring
• Theory of Preformation

  • Sex cells contain a complete miniature adult called a homunculus, perfect in every form
  • Several structures such as the alimentary canal were not initially present in the earliest embryos but instead were formed later during development
• Formation of male semen according to Aristotle

  Male semen is formed in numerous parts of the body and is transported through blood vessels to the testicles
• Cell theory

  All organisms are composed of basic visible units called cells, which are derived from similar preexisting structures
• Basic Concepts of Genetics

  Study of variation and heredity, focusing on similarities and differences among organisms and how characteristics are transmitted through generations
• Variations in Animals and Plants under Domestication

  Pangenesis - All cells produce gemmules which circulate around the body, gather in gonads, and determine the nature or form of each body part adaptively to an individual's external environment
• Fixity of Species

  Animal and plant groups remain unchanged in form from the moment of their appearance on earth
• Joseph Gottlieb Kolreuter (1733-1806) cross-bred two groups of tobacco and derived a new hybrid form, converted back to one of the parental types by repeated backcrosses, showing carnations exhibiting segregation of traits
• Francesco Redi (1621-1697), Lazzaro Spallanzani (1729-1799), Louis Pasteur (1822-1895) disproved the theory of spontaneous generation (Abiogenesis)
• Lamarck's Theory of Use and Disuse (1809) states that organisms acquire or lose characteristics that then become heritable
• All matter is composed of small invisible units called atoms
• The center of heredity in eukaryotic organisms is the nucleus, in prokaryotic organisms is the nucleoid region, and in viruses is the protein coat (viral head or capsid)
• Gregor Mendel (1866) established major postulates of transmission genetics as a result of experiments with the garden pea
• Evolution


  Existing species arose by descent with modifications from other ancestral species
• Gregor Mendel's 4 postulates
• Living organisms were considered to be derived from preexisting organisms and to consist of cells made up of atoms
• Theory of Natural Selection

  Survival of the fittest, adaptation to survive and reproduce, leading to reproductive isolation and the formation of new species
• The Theory of acquired inheritance was disproven