Prior to the 1860s, the passing down of traits like height, eye colour, and illness conditions were not well understood. Many assumed these traits appeared by chance, connecting them to “luck” and “chance”. This was until an Austrian monk named Gregor Mendel performed a series of experiments with pea plants to study how certain characteristics are inherited. His work revolutionised the understanding of heredity, laying the foundations for genetics as a true science.
In order to fathom the concept of heredity and the passing down of “genes”, Mendel crossbred pea plants that differed in distinct observable traits like flower colour, seed texture, and plant height. He chose pea plants as his ideal specimen due to their ability to self-pollinate reliably, exhibit multiple clear-cut variations, and germinate easily. From 1854 to 1856, he tested 34 varieties for constancy of their traits.
In his experiment, he allowed the hybrid offspring from his initial crosses to self-pollinate, and he closely tracked inherited traits through successive generations. He noticed that while his first generation F1 hybrids always expressed one parental trait, the subsequent F2 generation unexpectedly sorted the traits in predictable numerical ratios, like three purple-flowered plants for every one white among thousands of pea plants and over seven traits. This demonstrated that traits are inherited independently via internal discrete units, which we now know to be genes located on chromosomes. These traits are transmitted unchanged from parents to offspring, according to the fundamental principles of segregation and independent assortment that Mendel established through his innovative breakthroughs.
In modern days, Mendel’s research and findings can be sorted into two laws:
The first law is the law of segregation, which states that paired genes separate into different gametes during the formation of reproductive cells such that offspring receive one gene from each parent. For example, a pea plant with round and wrinkled genes would pass on either the round gene or the wrinkled gene to each offspring, but not both. This explained the 3:1 ratio of traits seen in experiments.
The second law is the law of independent assortment, which states that genes assort independently of each other during the formation of gametes such that traits are passed on independently. For example, a pea plant with green pods and round seeds could produce gametes with green/round, green/wrinkled, yellow/round or yellow/wrinkled combinations.
All in all, Gregor Mendel’s experiments showed that organism characteristics are inherited discretely rather than blending together. These distinct hereditary factors, now called "genes," are passed unchanged from parents to offspring. Genes from each parent randomly combine to produce new genetic variations. Mendel's work established basic rules of genetics, like dominance and segregation, that still guide our understanding of inheritance today.
Works Cited
Biology LibreTexts. (2018). 12.3A: Mendel’s Laws of Heredity. [online] Available at: https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/12%3A_Mendel's_Experiments_and_Heredity/12.03%3A_Laws_of_Inheritance/12.3A%3A_Mendels_Laws_of_Heredity [Accessed 28 Jan. 2024].
Gregor Mendel | Biography, Experiments, & Facts | Britannica. (2024). In: Encyclopædia Britannica. [online] Available at: https://www.britannica.com/biography/Gregor-Mendel [Accessed 28 Jan. 2024].
Nature.com. (2014). Gregor Mendel: A Private Scientist | Learn Science at Scitable. [online] Available at: https://www.nature.com/scitable/topicpage/gregor-mendel-a-private-scientist-6618227/ [Accessed 28 Jan. 2024].
Villanova.edu. (2024). About Mendel | Villanova University. [online] Available at: https://www1.villanova.edu/villanova/president/university_events/mendelmedal/aboutmendel.html [Accessed 28 Jan. 2024].
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