- Mendel's law of independent assortment states that alleles of different genes assort independently during gamete formation.
- This is explained by the random alignment of homologous chromosome pairs during metaphase I of meiosis, which leads to independent segregation, making (C) correct.
- (A) is incorrect because independent assortment applies mainly to genes on different chromosomes or those far apart on the same chromosome.
- (B) polygenic inheritance involves multiple genes influencing a trait, which is separate from independent assortment, so (B) is incorrect.
- (D) is incorrect because the law of independent assortment is demonstrated using dihybrid crosses.
Answer: \(\boxed{\text{C}}\)