Mendel used single gene (or monohybrid) experiments to describe his law of segregation. He used characters (or dihybrid) experiments to come up with what law?

Law of Independent assortment

Explanation:

Gregor Mendel, who was regarded the father of Genetics, discovered principles that governs inheritance in his experiments. He discovered that the alleles of a gene will separate into gametes when he performed a crossed involving a single gene or character like height, pea color etc. He proposed his law of segregation based on this.

However, he considered two characters or genes in his cross, which he called a DIHYBRID cross. He discovered that the alleles of each different gene separates into gametes independently of one another i.e. without one gene influencing the other in each gamete. He called this principle his LAW OF INDEPENDENT ASSORTMENT.

He obtained a 9:3:3:1 phenotypic ratio for the F2 dihybrid offsprings which is only possible if each gamete equally likely contains two alleles of the two different genes in different combinations.