Mendel’s laws of genetics
According to Mendel’s first law (the law of segregation), in each generation, two alleles of any gene present in the parent individual segregate into independent sex cells (e.g. into individual sperm) without undergoing any change and without affecting one another. The second law (the law of independent assortment of characters) states that the individual pairs of alleles of various genes segregate into sex cells independently of one another and that the manner of segregation of one pair of alleles in no way affects the segregation of another pair. In the first decades of the 20th century, geneticists demonstrated that Mendel’s second law applies only to pairs of genes, each of which belongs to a different chromosome (see also Why do elephants change faster than mice?).