Gregor Mendel a European Monk Born in 1822 Who Made Discoveries with Pea Plants That Established

Gregor Mendel The “Father of Genetics”

Gregor Mendel was a European monk born in 1822 who made discoveries with pea plants that established the basic laws of genetics.

Before Mendel, people believed in the “blending theory” or “blending inheritance”, which argued that offspring (children) are a blend of genetic material of both parents. This is like when you take two different colors of paints and blend them together to make a new color.

Based on the idea, populations would eventually begin to look alike. But, this does not happen. Also, according to the blending theory, certain traits would have to disappear because they would blend with another trait and become lost. Yet, this does not happen either. In fact, some traits, such as eye color, skip generations and reappear…

Mendel & his Pea Plants

In his experiments, Mendel used pea plants. He controlled their breeding very carefully. He made sure that his plants were true-breeding, that is, whenever the plants produced seeds, the offspring (children) would always produce plants exactly like the parents. For example, white pea plants would only produce white pea plants.

One day, Mendel crossed a purple true-breeding plant with a white true-breeding plant. That means he allowed the two plants (parents) to reproduce and produce new seeds (offspring). The purple and white parents produced all purple flowers (first generation).

Mendel thought this was interesting. He then allowed the purple offspring to cross and reproduce. To his surprise, he found that some of the purple offspring produce white flowers again! The trait for white color reappeared!

Mendel wondered what happened to the white plants after the purple and white plants were crossed. He hypothesized that the offspring had one genetic factor for purple flowers and one genetic factor for white flowers, but the purple factor had the ability to block the white factor. That is why the white factor could not be seen. A genetic factor that blocks another genetic factor is what is now called dominant. The dominant trait is observed when offspring have 1 or 2 dominant factors. The other factor that was blocked, the white factor, is now called recessive. Recessive factors are blocked by dominant factors. In order to see a recessive genetic factor, there must be 2 genetic factors present in the offspring.

Questions: 1. What does offspring mean? 2. What does “cross” mean? (the way “cross” is used in the reading) 3. How is a dominant factor different from a recessive factor? 4. How is the blending theory different from what Mendel discovered about genetic factors?