Gregor Mendel conducted experiments with pea plants to study heredity. He found that traits are passed from parents to offspring through discrete units (now known as genes and alleles). In his F1 hybrid offspring, dominant traits always appeared, but in the F2 generation the "lost" recessive traits reappeared in about 25% of plants. Mendel's work established the foundations of genetics and showed that heredity follows basic rules of dominance and segregation.