How the study of pea plants changed the way we think about life. The A, B, Peas… of Life!! How the study of pea plants changed the way we think about life. (Genetics Week 1)

Have you ever wondered why some family members look very similar while others look very different?

I Can… I CAN define the terms: trait, heredity, and genetics. I CAN describe the results of Mendel's crosses.

Heredity and Traits Traits are different forms of a characteristic. Heredity is the passing of traits from parent to offspring (children).

SON (offspring): Chris These are pictures of Peter, Lois, and Chris from Family Guy. SON (offspring): Chris DAD: Peter The term heredity describes the passing of traits from Peter and Lois to their offspring (son) Chris. MOM: Lois Which character traits does Chris have in common with his Dad or his Mom?

More on Heredity… Only certain traits can be passed from parent to offspring… For example, you might inherit your Dad’s hair color but you wouldn’t inherit the scar on his chin leftover from a painful football practice…

Gregor Mendel and Genetics Gregor Mendel (a 19th century monk), was the first person to study genetics (the scientific study of heredity).

Mendel’s Question Why are pea plant’s traits sometimes similar to their parents and sometimes very different?

Hmmm…the passing of traits must be controlled by something…right? Mendel’s Hypothesis Hmmm…the passing of traits must be controlled by something…right? Mendel hypothesized that something was being passed from parent to offspring to control the passing of traits--but how? And was there a pattern?

Mendel’s Experiment Mendel decided to “cross” two plants with different traits to see what traits the offspring would have. In his first experiment he “crossed” a tall plant with a short plant.

Mendel’s Experiment Mendel called this first generation of parent plants the parental generation or P generation. The tall and short pea plants he used were both purebred. Mendel used a paint brush to “cross-pollinate” the two plants. Have students make a prediction here. Tall or short? Or Both? Or middle? ?

Mendel’s Data In the second generation of pea plants, Mendel saw that all of the offspring were tall. He decided to cross this second generation (called F1 Generation) with each other to see what would happen. ?

Mendel’s Data But the next generation (F2 Generation) was more surprising! He had all tall plants except for one small plant!

Mendel Experiments Again (and again….) Mendel was so confused by the sudden re-appearance of the “short” trait, that he decided to do more experiments like this one but with different traits.

Mendel’s Next Experiment Violet vs. White Students should begin their mini-lab now.

Mendel’s Data In all of Mendel’s crosses, only one form of the trait showed in the F1 Generation. However, in the F2 Generation, the “lost” form of the trait always appeared in 1/4 of the plants.

Mendel’s Conclusions The “factors” that control each trait exist in pairs. The female parent contributes one factor, while the male parent contributes another factor. One factor in a pair can “hide” the other factor. (The “tall factor” hides the “short factor”.