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The history of Gregor Mendel's experiments and the birth of modern genetics.
Have you ever wondered why you might have your mother’s eyes but your father’s height? Or why two brown-eyed parents can sometimes have a blue-eyed baby? The answer was hidden in a small garden patch over 150 years ago.
In the 1850s, an Austrian monk named Gregor Mendel began studying how traits are passed from parents to offspring. At the time, people believed in 'blending inheritance'—the idea that a tall parent and a short parent would produce a medium-sized child. Mendel suspected this was wrong. He chose pea plants because they grow quickly, have easily identifiable traits (like flower color or seed shape), and their reproduction can be strictly controlled. By manually moving pollen from one plant to another, Mendel could track exactly which 'parents' produced which 'children' over many generations.
Quick Check
Why did Mendel choose pea plants instead of animals for his experiments?
Answer
Pea plants grow quickly, have clear observable traits, and their mating can be easily controlled by the researcher.
Mendel started with pure-breeding plants. When he crossed a pure-breeding purple-flowered plant with a pure-breeding white-flowered plant (the or Parent generation), the results were shocking. Instead of light-purple flowers, all the offspring (the generation) were dark purple. The white trait seemed to have vanished! Mendel realized that some traits are dominant (they mask others) and some are recessive (they are hidden when a dominant trait is present).
1. Start with two pure-breeding parents: Purple () and White (). 2. Cross them to create the generation. 3. Observe the result: Every single plant is Purple (). 4. Conclusion: Purple is the dominant trait.
Quick Check
If a trait is 'recessive,' does it mean it has disappeared from the plant's DNA forever?
Answer
No, it is simply hidden or 'masked' by the dominant trait and can reappear in later generations.
Mendel didn't stop at the first generation. He let the purple plants self-pollinate. In the next generation (), the white flowers suddenly reappeared! Specifically, for every 3 purple plants, there was 1 white plant. This led to the Law of Segregation: Every individual has two 'factors' (now called alleles) for each trait, which separate during the formation of reproductive cells. An offspring receives one allele from each parent. This mathematical ratio proved that inheritance isn't a messy blend; it's a precise calculation.
In the generation, Mendel counted 929 plants. 1. Total plants = 929 2. Purple plants observed = 705 3. White plants observed = 224 4. Calculate the ratio: 5. This confirms the theoretical ratio expected from the Law of Segregation.
Mendel is called the Father of Genetics because he was the first to apply mathematics to biology. He realized that traits are inherited as discrete 'particles' (which we now call genes) that do not change or blend. Although his work was ignored during his lifetime, it eventually became the foundation of modern biology. He proved that inheritance follows predictable laws, allowing us to use probability to determine the likelihood of traits appearing in future generations.
Imagine you have a mystery pea plant with purple flowers. You know purple () is dominant over white (). 1. If you cross it with a white plant () and all offspring are purple, the mystery plant was likely . 2. If half the offspring are white (), the mystery plant must have been . 3. This is called a test cross, a method still used by scientists today to determine an organism's genetic makeup.
What ratio of dominant to recessive traits did Mendel consistently find in the generation?
Which term describes a trait that is hidden when a stronger trait is present?
Mendel used the term 'DNA' to describe the units of inheritance he discovered.
Review Tomorrow
In 24 hours, try to explain the Law of Segregation to a friend using the ratio as evidence.
Practice Activity
Look at your own family. Are there any traits (like a hitchhiker's thumb or detached earlobes) that seem to 'skip' a generation? This is Mendel's laws in action!