History of Genetics

• Early Beliefs of Heredity

  • Particulate Theories
  • Preformationist theories
• Particulate Theories


  • Information from each part of the parent had to be communicated to create an offspring
  • Attempts to explain observed similarities between parents and children
  • Were inaccurate because no microscope
• Preformationist theories


  • Proposed about reproductive cells that contained offspring
• Epigenesists


  A process described by Aristotle in which offspring is gradually generated from an undifferentiated mass by addition of parts
• Aristotle's important contribution is his conclusion that inheritance involved the potential of producing certain characteristics rather than absolute production of characteristics themselves
• Charles Darwin and Alfred Russel Wallace announced the theory of evolution


  1858
• Darwin posited that cells reproduce themselves
• Improvements in microscopy and the increasing study of cytology enabled the scientist to identify parts of the cell
• Cell


  The basic unit of life, all living things are made up of cells
• Cell Theory


  1. Robert Hooke's observation of honeycomb patterns in cork

  2. Rene Dutrochet's microscopic studies concluding that both plants and animal tissues are composed of cells

  3. Matthias Jakob Schleiden's theory that all plants were constructed of cells

  4. Theodor Schwann's suggestion that animals were also composed of cells
• Schwann and Schleiden both described cells as the basic unit of life and that all living things are made up of cells
• German pathologist Rudolf Virchow launched the theories of biogenesis when he posited that cells reproduce themselves
• Germplasm theory of heredity

  Asserted that for each organism was contained germ cells (cells that create sperm and eggs)
• Augutst Weissman theorised reduction division or Meiosis
• Gregor Mendel


  A farmer's son who became the father of genetics
• Mendel's Experiments


  1. Conducted 30,000 experiments on pea plants

  2. Chose pea plants because of their distinct, and identifiable characteristics

  3. Raised several generations of self fertilized plants and each variety were tended to be pure breed

  4. Designed experiments to test inheritance of a specific trait from one generation to the next
• Mendel's Theories


  • Trait come in pairs - one from each parent
  • One trait will assume dominance over the other
  • Combination of traits will then create an offspring that is different entirely to the original trait
• Mendel's theories were not acknowledged during his lifetime, it was in the 20th century that the scientific community acknowledged the importance of his ideas
• Johann Friedrich Miescher identified nuclein, a substance in the white blood cells
• Miescher separated nuclein into a protein and an acid and it was renamed nucleic acid
• Karl Erich Correns, Hugo Marie de Vries, and Eric von Tschermak-Seysenegg rediscovered Mendel's principles of heredity and acknowledged mendel's contribution to modern genetics
• Archibad E. Garrod applied Mendel's principles to identify the first human disease about genetics which is called "alkaptonuria", or the inborn errors of metabolism
• Genetics


  Term coined by Willian Bateson, along with other terms such as allele, zygote, homozygote, and heterozygote
• Bateson's most important contribution is his translation of Mendel's work from German to English and his endorsements on Mendel's principles
• Hardy-Weinberg equilibrium


  A mathematical formula that describes the actions of genes in populations, enables geneticists to determine whether evolution is occurring in populations
• Garod published Inborn Errors od Metabolism which descired various diseases caused by inborn metabolism errors such as Albinism and Porphyria
• Chromosome theory of Inheritance


  • Walter Stanborough Sutton's research demonstrated that chromosomes exist in pairs that are structurally similar and that sperm cell and egg cell have one pair of chromosomes
  • Sutton's work advanced genetics by identifying relationship between Mendel's laws of heredity and the role of the chromosome in Meiosis
• Thomas Hunt Morgan


  Often referred as the "Father of Clasical Genetics"
• Morgan's Research


  1. Performed laboratory research on fruit flies

  2. Confirmed the Findings of Mendel, Bateson, and Sutton

  3. Produced the Chromosomal Theory of Inheritance which states that genes are the fundamental units of inheritance and are found on chromosomes, and that specific genes are found on specific chromosomes and are not always inherited together
• Morgan, Bridges, Muller, and Sturtevant published The mechanism of Mendelian Heredity
• Morgan asserted that the ability to quantify or numbers gene enables the researchers to predict accurately the distribution of specific traits and characteristics
• Calvin Blackman Bridges eventually discovered the first chromosomal deficiency as well as chromosomal duplication in fruit flies
• Phoebus A. Levene isolated and discovered the structure of the individual units of DNA called nucleotides
• Theophillus Shickel made the first estimate of the number of Human Chromosomes, his count was 48
• Martha Cowles Chase and Alfred Day Hershey conducted experiment that provided a definitive proof that DNA was a genetic material, known as the "Waring Blender Experiment"
• Alfred H. Sturtevant


  Often referred to as the father of Human Genome Project, published the comprehensive map of Humanity's 20,000 to 25,000 genes
• Barbara McClintock described key methods of exchange of genetic information, such as Crossing over or recombination
• Fredrick Griffith's experiments on Streptococcus pneumoniae offered the first tangible evidence linking DNA to heredity in cells
• Oswald Theodore Avery, Colin Munro Macleod, and Maclyn McCarty performed studies demonstrating that Griffith's transforming factor was DNA rather than simply a protein, confirming that DNA was the molecular basis for genetic information
• In 1953, James D. Watson and Francis Crick famously described the structure of DNA, marking the birth of Modern Genetics