Gregor Mendel's discoveries

  • Guanine discovered

    guanine, which is one of the bases of DNA and RNA, was first discovered in guano in 1846 and was isolated in 1891
  • Mendel's Laws of Inheritance are discovered

    Between 1856 and 1863 Mendel cultivated and tested some 29,000 pea plants. This study showed that one in four pea plants had purebred recessive alleles, 25% were hybrid and 75% dominant. His experiments led him to make two generalizations, the Law of Segregation and the Law of Independent Assortment, which later became known as Mendel's Laws of Inheritance.
  • Mendel publishes his work in Proceedings of the Natural History Society of Brunn

  • DNA first isolated

    DNA was first isolated by the Swiss physician Friedrich Miescher who, in 1869, discovered a microscopic substance in the pus of discarded surgical bandages.
  • Mitosis discovered

    The first person to discover and study mitosis was Walther Flemming in 1870. Mitosis is the reproduction of body cells
  • Oscar Hertwig discovers meiosos

    Meiosis was discovered and described for the first time in sea urchin eggs in 1876 by the German biologist Oscar Hertwig.
  • Mendel's Law of Segregation discovered

    The direct proof of this was later found following the observation of meiosis by two independent scientists, Oscar Hertwig in 1876, and Edouard Van Beneden The law of segregation consists in that when any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy.
  • Cytosine discovered

    Cytosine is one of the four main bases found in DNA and RNA.
    It was discovered by Albrecht Kossel when it was hydrolysed from calf thymus tissues. A structure was proposed in 1903, and was synthesized in the laboratory in the same year.
  • Thomas Hunt Morgan realeases his the chromosome theory of inheritance

    The chromosome theory of inheritance is a fundamental unifying theory of genetics which identifies chromosomes as the carrier of genetic material.
  • Phoebus Levene identified the base, sugar and phosphate nucleotide unit

    Levene suggested that DNA consisted of a string of nucleotide units linked together through the phosphate groups.
  • William Astbury produced the first X-ray diffraction

    by the first x-ray diffraction, William discovered that DNA had a regular structure
  • Punett square is invented

    Reginald Punnett invents the punnet square to determine the posibilities of genotypes appearing in a organism
  • DNA identified as the transforming principle

    Oswald Avery, along with coworkers Colin MacLeod and Maclyn McCarty, identified DNA as the transforming principle.
  • Chargaff's rules

    Chargaff discovered that adenine (A) always equals thymine (T) and that guanine (G) always equals cytosine (C) in DNA. This was discovered near the 50's decade
  • DNA's role in heredity confirmed

    Alfred Hershey and Martha Chase in the Hershey–Chase experiment showed that DNA is the genetic material of the T2 phage.
  • Rosalind Franklin and Raymond Gosling take x-ray images of DNA

    Rosalind Franklin and Raymond Gosling worked together and took some x-rays of DNA. The DNA crystallography allowed Watson and Crick to find out it was a double helix.
  • James D. Watson and Francis Crick discover the structure of a DNA

    James Watson and Francis Crick discover the DNA structure of all species comprises two helical chains each coiled round the same axis looking like a twisted ladder, and each with a pitch of 34 Ångströms and a radius of 10 Ångströms.
  • Francis's Cricks presentation

    Crick laid out the central conclutions of molecular biology describing the relationship between DNA, RNA, and proteins
  • Nobel Prize in Physiology or Medicine for Watson, Cricks and Wilkins

    In 1962, after Franklin's death, Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine.
  • Seymour Kessler categorizes the phases of counseling

    Seymour Kessler, in 1979, first categorized sessions in five phases: an intake phase, an initial contact phase, the encounter phase, the summary phase, and a follow-up phase. Counseling is is the process by which patients are advised of the consequences and nature of the disorder