Assertion (A) : Gametes receives only one allele of a gene.
Reason (R) : Mitosis occurs during gamete formation leading to the formation of haploid gametes.

Meiosis occurs during the process of gamete formation which leads to the formation of haploid gametes.
Though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors.