(a): If in a dihybrid test cross more parental combinations appear as compared to the recombinants in $F_2$ generation, then it is indicative of involvementof linkage. Linkage is the tendency of two differentgenes on the same chromosome to remain together during the separation of homologous chromosomes at meiosis. During complete linkage no recombinants are formed whereas in incomplete linkage few recombinants are produced along with parental combinations.