The P1 (or P) generation, or parental generation, refers to the first set of individuals in a genetic cross that are mated to produce offspring.

In a classical Mendelian genetics experiment, the P1 generation is usually comprised of two individuals that are homozygous for a particular trait, meaning they have two identical copies of the gene that controls that trait.

When the P1 generation is crossed, their offspring are referred to as the F1 generation (first filial generation). The traits that are observed in the F1 generation are then used to make predictions about the genetic makeup of subsequent generations.

The predictions are based on Mendel’s laws.

The P1 generation is important in genetics as it establishes the genetic traits that are being studied in a particular experiment or cross. By selecting individuals with known genetic traits, researchers study the patterns of inheritance and the transmission of genetic traits from one to the next generations.

P1 generation
Image: Illustration demonstrating a cross between two parents that differ by two homozygous traits each (short black hair vs. long brown hair) | carlsonstockart.com