History of genetics

• Gregor Mendel (mid 19th century) carried out experiments crossing (mating) plants with different characteristics.
• By observing the characteristics of the offspring produces, Mendel was able to draw conclusions about the inheritance of characteristics
• Even though Mendel didn't know about chromosomes or genes he was able to conclude:

  • Characteristics are determined by factors within the organism (now known to be genes.)
  • that the factors (genes) can be present in two different forms. (now known as alleles.)
  • the the two factors (alleles) in an individual sperate during gamete formation (now known as meiosis)
• Mendel's work, however, was not accepted by scientists when he was alive for three main reasons:

  • when he presented his work to other scientists he did not communicate it well so they did not really understand.
  • it was published in a scientific journal that was not well known so no many people read it
  • he could not explain the science behind why characteristics were inherited.
• late 19th century:

  the idea that genes were located in chromosomes emerged when better microscopes and staining techniques allowed scientists to visualize the behavior of chromosomes during cell division.
• Early 20th century:

  it was observed that chromosomes and Mendel's 'units' behaved in similar ways. this lead to the theory that the 'units', now called genes, were located in chromosomes.
• 1944:

  Oswald Avery transferred DNA between bacteria. the DNA transferred was linked to the ability cause disease. he saw that this trait was then passed on to the offspring and concluded genes are made of DNA.
• 1950:

  Erwin Chargaff found that even though different organisms have differed amounts of DNA, all DNA contained equal amounts of adenine and thymine, and of cytosine and guanine.
• 1953:

  James Watson and Francis Crick worked out the structure of DNA. by using data from Rosalind Franklin and Maurice Wilkins, Watson and Crick were able to build a model of DNA. they showed that bases occurred in pairs, and X-ray data showed that there were two chains wound into a double helix. this model was used to work out how genes code for proteins
• 2003:

  the Human Genome Project started in 1990 and was completed in 2003. hundreds of scientists from different universities all over the world collaborated together to determine the sequence of base pairs that made up the genome of a random man and woman. the mapping of the whole human genome has great importance for medicine. in order to exploit its secrets, it is vital that the human genome is fully understood. it enables us to:

  • search for genes linked to different types of genes
  • understand inherited disorders and their treatment
  • trace human migration patterns from the past.