Which of Mendel's laws or principles states that gametes carry one allele for each trait?

The law or principle by Gregor Mendel that states that gametes carry one allele for each trait is his first law, the law of segregation. This law governs heredity and states that allele pairs separate or segregate when the gametes are formed and they unite randomly during fertilization.

gamete contains only one set of chromosome and thus, carry one allele for each characteristic. This principle was defined by Mendel in his first law, i. e. the law of segregation. During meiosis, alleles segregate and each one contains one trait. Thus, the offsping receives a pair of an allele, for a trait.