Advanced Placement (AP) Biology Practice Exam

Which generation do the phenotypic traits first appear in Mendelian inheritance?

1. F2 generation

2. P generation

3. F1 generation

4. Hybrid generation

The correct answer is: F1 generation

In Mendelian inheritance, the phenotypic traits first appear in the F1 generation, which is the first filial generation resulting from a cross between two parental (P) generation organisms with different traits. In this generation, offspring exhibit the dominant trait if one is present, demonstrating the principles of dominance discovered by Gregor Mendel. For example, if a purebred tall plant is crossed with a purebred short plant, all the offspring in the F1 generation will be tall if tall is the dominant trait. The P generation represents the initial parents with distinct traits, and while those traits are important for determining the inheritance patterns, they do not exhibit the hybrid traits that result from crossing. The F2 generation emerges from the self-fertilization or crossing of the F1 generation and is where the phenotypic ratio showcasing both dominant and recessive traits can be observed. Therefore, it is the F1 generation that first expresses the distinct phenotypic traits derived from the parental genotypes.