What did mendel discover about recessive traits?

Gregor Mendel discovered that recessive traits are expressed only when an individual has two copies of the recessive allele, one inherited from each parent. In cases where a dominant allele is present, the dominant trait masks the expression of the recessive trait. Mendel's experiments with pea plants illustrated this concept, leading to the formulation of the laws of inheritance. His work laid the foundation for understanding genetic inheritance patterns.