Which one of the following statements is correct for Law of Dominance?

The correct answer is Option (3) → Characters are controlled by discrete units called factors, which occur in pairs.

Mendel proposed three rules from his crosses. The Law of Dominance has three parts: (i) characters are controlled by discrete units called factors; (ii) factors occur in pairs; (iii) in a dissimilar pair of factors one member dominates the other. It explains why only one parental character shows in the F₁ and the 3:1 ratio in the F₂.

(1) This law is based on the fact that the alleles do not show any blending. — Incorrect. This describes the Law of Segregation. Both characters are recovered as such in the F₂ generation, though one of them is not seen in the F₁.

(2) When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters. — Incorrect. This is the Law of Independent Assortment, which comes from dihybrid crosses.

(3) Characters are controlled by discrete units called factors, which occur in pairs. — Correct. These are the first two parts of the Law of Dominance.

(4) The factors or alleles of a pair segregate from each other in such a way that a gamete receives only one of the two factors. — Incorrect. This too belongs to the Law of Segregation. It is why each gamete is pure for one allele.

NCERT Extract:
Law of Dominance –