the Mendel's first law?
A Mendel's first law postulates that a characteristic (trait) of an individual is always determined by two factors, one inherited from the mother and the other from the father and the direct offspring of the individual receives from it only one of these factors (aleatory). In other words, every trait is determined by two factors that segregate during gamete formation.
The Mendel's first law is also called as the law of purity of gametes. The Mendel deduced the way genes and alleles were transmitted and traits were conditioned without even knowing of the existence of these elements