Genes are the basic unit of heredity and continuous stretch of DNA which are linearly arranged on chromosomes. Alleles are the alternative form of the gene that occupies the same locus on homologous chromosomes and therefore governs the same trait. The alleles for a gene are segregated and delivered singly to gametes by the process of segregation of homologous chromosomes during anaphase-I of meiosis. Thus, each gamete receives single allele of a gene. Owing to their haploid status, gametes carry one complete set of chromosomes which in turn carry the single allele for each gene. Thus, the correct answer is option A.