Mendel's law of independent assortment was best demonstrated when he crossed true-breeding plants and followed two traits at a time. What did he observe when following two traits that helped him formulate this law?a. He observed that the wrinkled and smooth traits always blended to produce semi wrinkled seeds.b. He observed that the dominant traits are always inherited together and the recessive traits are always inherited together; no offspring displayed one dominant and one recessive trait.c. All of the answers are correct observations.d. He observed that both dominant traits always hid the recessive traits in these double crosses.e. None of the answers are correct observations.

The observation that the dominant traits hid the physical expression of recessive traits in dihybrid cross helped Mendel to formulate the law of independent assortment of genes.

The law of independent assortment of genes states that traits are inherited independently of one another without any form of interference.

For example, the trait for height (T, tallness is dominant over t, shortness) and seed shape (smooth, S is dominant over wrinkle, s) will be independently inherited in a cross involving the two traits.

The ratio of tall individuals to short individuals and that of smooth individuals to wrinkle individuals at F2 will both be 3:1, which is the same standard ratio that will be obtained if the traits are considered independently.

The correct option is d.