Explanation

Types of gametes $= 2^{n}$ n=Number of heterozygotes considered, i.e., monohybrid cross(n =1), dihybrid cross (n =2), trihybrid cross (n =3) and so on. AA BB CC $\times$ aa bb cc is a trihybrid cross, therefore, different types of gametes are $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 2^{n}$ $= {(2)}^{3}$ $= 2 \times 2 \times 2 = 8$