(GIST OF SCIENCE REPORTER) MENDEL’S LAW OF INHERITANCE

(JULY-2025)

MENDEL’S LAW OF INHERITANCE

Context:

Scientists have finally resolved the 160-year- old genetic mystery behind Mendel’s pea plant traits by identifying the specific genes responsible for the last three uncharacterized traits.

Mendel’s Pioneering Work on Pea Plants

Experimental Period and Scope: Gregor Johann Mendel began his experiments on pea plants (Pisum sativum) in 1856, diligently working for eight years on more than 10,000 plants to understand trait inheritance.
Sixteen years after Mendel’s death in 1884, in the year 1900, three scientists—Hugo de Vries, Carl Correns, and Erich von Tschermak—independently rediscovered his work. They realised that Mendel had indeed answered the question of whether parental traits are passed on with varying frequencies.

Key Observations and Discoveries

Mendel studied the inheritance patterns of seven traits in pea plants, each having two clearly distinguishable forms. These traits included:

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)
Dominance in F1 Generation: He observed that when crossing plants with opposing traits, one form consistently dominated the other. For instance, crossing round-seeded and wrinkled-seeded plants always produced first-generation (F1) offspring with round seeds.
3:1 Ratio in F2 Generation: In the second generation (F2) produced by crossing two first-generation plants, the previously hidden form (e.g. wrinkled) reappeared at a lower frequency, consistently showing a 3:1 ratio of dominant to recessive traits (e.g. round to wrinkled seeds).

Impact on Genetics

Mendel’s work laid the foundation for modern genetics by showing that:

Traits are inherited through discrete units (now called genes).
Each organism carries two alleles for every gene, one from each parent.
These alleles may be dominant or recessive, and inheritance follows predictable patterns.
His work later contributed to the chromosome theory of inheritance.

Century-Old Genetics Mystery Solved

Unanswered Questions: Despite the profound impact of Mendel’s work, the specific genetic differences responsible for the two forms of his seven studied traits remained unanswered for a long time, taking 108 years for the scientific community to fully understand.

Key Findings from the New Study

Genetic Complexity of Pisum Genus: While traditionally thought to comprise four species, genetic analysis revealed that the genus Pisum actually forms eight genetic groups, with the four species distributed across these groups due to extensive crosses and admixtures. This indicates a more complex population structure than previously recognised.

Identification of Genes for Remaining Traits: The study successfully identified the genes involved in the three previously uncharacterized traits:
Pod colour: A deletion of a segment of DNA before the ChlG gene disrupts chlorophyll synthesis, leading to yellow pods.
Constricted pod shape: Changes near the MYB gene combined with changes in CLE-peptide-encoding genes result in this trait.
Flower position (at the end of the stem): A small deletion in the DNA containing the CIK-like-coreceptor-kinase gene, along with a modifier locus, is associated with this characteristic.