Mendel conducted self-pollination experiments with both the parental plants and the F1 tall plants. When the F1 tall plants were allowed to reproduce through self-pollination, the resulting second-generation, or F2, progeny exhibited a mix of tall and short plants. This testing process helped determine if the traits were inherited and how they expressed in subsequent generations.
How did Mendel test whether the tall plants in the F1 generation were exactly the same as the tall plants of the parent generation?
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Mendel tested whether the tall plants in the F1 generation were exactly the same as the tall plants in the parent generation through a test cross. Initially, he established a pure-breeding parental generation, one with the trait for tallness (TT) and another with the trait for shortness (tt). Upon crossing these true-breeding plants, the F1 generation exhibited all tall plants, suggesting dominance of the tall trait. To investigate the genetic composition of the F1 tall plants, Mendel performed a test cross by crossing an F1 tall plant (Tt) with a true-breeding short plant (tt). If the F1 tall plants were pure-breeding for tallness, all offspring in the F2 generation would be tall. However, if the F1 tall plants carried the recessive trait for shortness, a 1:1 ratio of tall to short plants would emerge in the F2 generation. Mendel observed approximately 25% short plants in the F2 generation, confirming that the F1 tall plants were not identical but heterozygous for the tall and short traits. This test cross provided crucial evidence for Mendel’s laws of inheritance.