In dihybrid inheritance, Mendel considered

Step 1: Analyze the question The question asks how many pairs of contrasting characters (traits) Mendel considered in a dihybrid cross.

Step 2: Explain the concept The prefix tells you the answer:

• Monohybrid = one pair of contrasting characters (e.g., tall vs. dwarf plants)
• Dihybrid = two pairs of contrasting characters (e.g., seed shape and seed colour together)
• Trihybrid = three pairs

Step 3: Work through the solution In his dihybrid experiments with garden peas, Mendel crossed plants that differed in two traits at the same time:

• Seed shape: round (R) vs. wrinkled (r)
• Seed colour: yellow (Y) vs. green (y)

• Parents: RRYY (round, yellow) × rryy (wrinkled, green)
• F1: all RrYy (round, yellow)
• F2 phenotypic ratio: 9 : 3 : 3 : 1 • 9 round yellow • 3 round green • 3 wrinkled yellow • 1 wrinkled green

This led to his Law of Independent Assortment: the factors for different characters separate independently of one another during gamete formation.

Step 4: Identify the answer Dihybrid inheritance involves two pairs of contrasting characters, so the answer is B.

Tip: Let the prefix guide you. "Di" means two, so a dihybrid cross involves two pairs of traits. Also remember that 9:3:3:1 is the signature F2 ratio of a dihybrid cross, and 3:1 is that of a monohybrid cross.