Final answer:
During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. So, the correct answer is option a.
Step-by-step explanation:
Mendel's law of independent assortment states that genes do not influence each other with regard to the sorting of alleles into gametes, and every possible combination of alleles for every gene is equally likely to occur. During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. This process is explained by the first division of meiosis, in which homologous chromosomes with their different versions of each gene are segregated into daughter nuclei.
So, the correct answer is option a.