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Gregor Mendel and the Foundations of Genetics
Scientists finally solve the 160-year-old problem of Mendel’s peas
Context: In 1900, three scientists rediscovered Mendel’s work and realised he had already shown that some traits are passed from parents to offspring more often than others. His experiments with pea plants explained how traits are inherited.
Origins of Modern Genetics
- In 1856, Gregor Johann Mendel, an Austrian monk, began experiments on pea plants to understand how traits are inherited.
- He worked for eight years, experimenting on over 10,000 plants.
- In 1865, Mendel presented his results to the Brunn Natural History Society.
- His findings were published in 1866 in the society’s journal, Proceedings of the Natural History Society of Brno.
- Mendel’s work received little attention during his lifetime. He died in 1884, unaware of his future legacy.
Rediscovery and Validation
- In 1900, 16 years after Mendel’s death, three scientists — Hugo de Vries, Carl Correns, and Erich von Tschermak — independently rediscovered his work.
- They confirmed Mendel had explained how certain traits are passed on more frequently than others.
- Mendel studied seven traits, each with two contrasting forms:
- Seed shape – round or wrinkled
- Seed colour – yellow or green
- Flower colour – purple or white
- Pod shape – inflated or constricted
- Pod colour – green or yellow
- Flower position – along the stem or at the end
- Plant height – tall or short
- Observation: Crossing plants with different traits (e.g., round vs. wrinkled seeds) resulted in offspring with dominant traits (e.g., round seeds).
- When these offspring were crossed, the recessive trait (e.g., wrinkled seeds) reappeared in a consistent 3:1 ratio in the second generation.
Birth of Genetics
- Mendel’s work established that traits are inherited via discrete units, now called genes.
- Later discoveries:
- Each organism has two versions (alleles) of each gene — one from each parent.
- Dominant alleles can mask the effect of recessive ones.
- These patterns led to the chromosome theory of inheritance and modern genetic science.
- The Missing Pieces: Despite early success, genetic causes of three traits (pod colour, pod shape, flower position) remained unresolved for over a century. By 1917, researchers began identifying genetic locations, but complete understanding took 108 more years.
The 2024 Breakthrough
- On April 23, 2024, the mystery was finally solved. A study published in Nature reported the identification of the genetic factors responsible for the last three of Mendel’s seven traits, as well as new insights into the four already-characterised traits.
- To achieve this, scientists analysed more than 697 well-characterised pea plant variants using next-generation sequencing, yielding a staggering 60 terabases of DNA — equivalent to nearly 14 billion pages of text, or a stack of A4 paper stretching 700 kilometres high.
- Buried within this mountain of data were the answers Mendel had unknowingly sought over a century ago.
Key Findings
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- Complex Genetic Grouping: Although the pea plant genus Pisum is generally accepted to include four species, genetic analysis revealed eight distinct groups. These arose due to multiple crosses and admixtures, indicating a more complex population structure than previously known.
- New Allelic Variants Identified: For four of Mendel’s traits—seed shape, seed colour, flower colour, and plant height—new contributing alleles were discovered.
- For example, a new variant found in white-flowered plants causes them to produce purple flowers, demonstrating that trait expression is more intricate than Mendel’s observations suggested.
- Genetic Basis of the Final Three Traits Uncovered:
- Pod Colour: A DNA deletion before the ChlG gene disrupts chlorophyll synthesis, turning green pods yellow.
- Pod Shape: Changes near the MYB gene and CLE-peptide-encoding genes result in constricted pods.
- Flower Position: A small deletion involving the CIK-like-coreceptor-kinase gene, along with a modifier locus, causes flowers to appear at the end of the stem.
- Wider Genomic Insights: The comprehensive genomic map also revealed interactions beyond Mendel’s original scope. These included 72 agriculturally important traits related to seed, pod, flower, leaf, root, and overall plant architecture.
Implications for the Future
- With the closure of this 160-year-old scientific quest, the door is now open to a new era in plant genetics. The depth of genetic information revealed by this study holds immense potential for:
- Improving crop yield
- Enhancing disease resistance
- Adapting plants to changing climates
- It is nothing short of remarkable that such vast scientific progress traces its roots to a 19th-century monk, who, while tending to his garden, had the curiosity to ask why.
