Gregor Mendel

• Genes


  Sections of DNA on a chromosome that determine the amino acid sequence of a specific protein
• Alleles


  Different versions of a gene
• Dominant allele


  An allele that is expressed even if only one copy is present, e.g. the allele for polydactyly
• Recessive allele


  An allele that is only expressed if two copies are present, e.g. the allele for cystic fibrosis
• Gregor Mendel


  • Carried out thousands of breeding experiments on pea plants
  • Realized that characteristics are determined by inherited units (genes) that do not change when passed on to descendants
• At the time, scientists believed that characteristics were blended when inherited
• Mendel published his research in a scientific paper, but it was not recognized until later
• Scientists looked at how chromosomes behaved during cell division


  Late 1800s
• Scientists rediscovered Mendel's work and realized that Mendel's units (genes) behaved in a similar way to chromosomes


  Early 1900s
• Scientists determined the structure of DNA and how genes function

  Mid 1900s
• Mendel's units were renamed genes
• Scientists realized that genes must be located on chromosomes
• There will be plenty of questions on Mendelian genetics in the revision workbook