Genetics Timeline

  • Gregor Mendel

    Gregor Mendel
    Mendel performed an experiment on pea plants. First he prevented self fertilization by cutting off the stamens from purple flowers. Then he transferred pollen from the stamen of a white folower to the purple one. The result was all the flowers were purple. He self bred the new generation with itself and found that three-fourths of the offspring were purple. With this, he determined that plants had different alleles and two genes from each parent. Only one allele was fully expressed.
  • William Bateson and Reginald Punnett

    William Bateson and Reginald Punnett
    Bateson and Punnett crossed two doubly heterozygous plants that exhibited dominant traits. The results did not match the predicted 9:3:3:1 ratio of a dyhybrid cross. Together they introduced the punnett square and they discovered linked genes.
  • Thomas Hunt Morgan

    Thomas Hunt Morgan
    Morgan bred fruit flies to see patterns in breeding. The found that white eyes were only found on male flies. With this he discovered sex-linked genes and crossing over. He was also able to map genes with recombination frequencies.
  • Archibald Garrod

    Archibald Garrod
    Garrod observed people with alkaptonuria conjestional disorder. When exposed to light, the patients' urine turned dark. With that he was able to suggest that genes dictate phentoypes through enzymes, the proteins that catalyze chemical processes.
  • Frederick Griffith

    Frederick Griffith
    He used different types of pneumonia bacteria, one lethal and one harmless. He heated the lethal bacteria up and injected it into a mouse. In result, the mouse did not die. Then he mixed the heated bacteria with the harmless bacteria together and it killed the mouse. He discovered that DNA controls the cells.
  • George Beadle and Edward Tatum

    George Beadle and Edward Tatum
    Using orange bread mold, they studied that they were unable to grow on the usual simple growth medium. Each mutuant turned out to lack an enzyme in metabolic pathway that produce some molecules that the mold needed. They formed the one gene - one enzyme hypothesis which stated that the function of an individual gene is to dictate the production of a specific enzyme.
  • Erwin Chargaff

    Erwin Chargaff
    Chargaff noticed a pattern in the model and took samples of different DNA cells to find out Chargaff's Rules. These rules stated that the amount of adenine is equal to the amount of thynine and that the amount of guanine is equal to the amount of cytosine.
  • Alfred Hershey and Martha Chase

    Alfred Hershey and Martha Chase
    First they injected radioactive protein into bacteria then tested for radioactivity. They saw that the radioactivity was in the liquid but not the pellet. Then the performed the same experiment but instead injected the bacteria with radioactive DNA and found that the radioactivity was in the pellet, not the liquid. This demonstrated that DNA is the genetic material to a bacteriophage called T2.
  • Maurice Wilkins and Rosalind Franklin

    Maurice Wilkins and Rosalind Franklin
    Wilkins and Franklin were the first people to take a picture of DNA using crystalline x-ray diffraction and discovered that DNA was a helix.
  • James Watson and Francis Crick

    James Watson and Francis Crick
    They studied protein structure with x-ray crystallography. From the picture they determined that the helix had a diameter of 2nm. The also discovered that DNA was a double helix and that A pairs with T and G pairs with C.
  • Marshall Nirenberg

    Marshall Nirenberg
    Nirenberg produced RNA composed of Uracil. Then he added the RNA into a cell free extract of Escherichia coli which contained DNA, RNA, Ribosomes, and other cellular machinery for protein synthesis. After that he added DNase, 1 radioactive amino acid, and 19 unlabeled amino acids to the extract. The result was a radioactive protein. Nirenberg was able to breack the genetic code and describe how it operates in protein synthesis.