Which of the following correctly represents the law of segregation?
- A9 : 3 : 3 : 1
- B3 : 1
- C1 : 1
- D1 : 2 : 1
Show answer and explanation
Correct answer: (b) 3 : 1
Explanation
The law of segregation says that the two factors (alleles) for a trait separate when gametes form, so each gamete carries only one of them.
Mendel saw this in a monohybrid cross: crossing tall (TT) and dwarf (tt) pea plants gives all tall (Tt) plants in F₁, and selfing them gives tall and dwarf plants in the 3 : 1 phenotypic ratio in F₂. The dwarf trait reappears because the alleles separated. The genotypic ratio in F₂ is 1 : 2 : 1.
The 9 : 3 : 3 : 1 ratio of a dihybrid cross shows the law of independent assortment.