The Understanding of Genetics (AQA GCSE Biology): Revision Notes

6.3.3 The Understanding of Genetics🧬

Gregor Mendel

• Background: Gregor Mendel was trained in mathematics and natural history in Vienna, which equipped him with the skills needed for his pioneering work in genetics.
• Experiments in the Monastery Gardens: While working in the monastery gardens, Mendel conducted extensive breeding experiments on pea plants. He carefully observed how traits were passed from one generation to the next.
• Key Experiments: Mendel experimented with various types of pea plants, including smooth peas, wrinkled peas, green peas, and yellow peas. By observing the traits of their offspring, he made several groundbreaking discoveries about inheritance.

• Mendel's Conclusions:
  • Traits are inherited through what Mendel called "hereditary units," which are now known as genes.
  • Offspring inherit one hereditary unit from each parent.
  • These units can be dominant or recessive and do not blend together but are passed on intact.

Recognition and Later Discoveries

• Delayed Recognition: Mendel's work was not widely recognised during his lifetime because the concepts of genes and chromosomes were not yet understood, making it difficult for others to grasp his findings.
• Advancements in the Late 19th Century:
  • Scientists began observing chromosomes as part of the process of cell division.
• 20th Century Breakthroughs:
  • It was discovered that chromosomes behaved in a way similar to Mendel's hereditary units, leading to the realisation that these units (now called genes) were located on chromosomes.
• Discovery of DNA Structure (1953): The structure of DNA was determined by James Watson and Francis Crick, which provided the molecular basis for understanding how genes work, solidifying Mendel's earlier findings.