Maximizing Proportion of Recessive Brown Fur Offspring

Steps:

• Brown fur requires homozygous recessive genotype (bb); black fur appears in any genotype with B (BB or Bb).
• Evaluate offspring genotypes for each cross using Punnett squares or Mendelian ratios.
• Cross A (BB x BB): All offspring BB (100% black).
• Cross B (BB x Bb): 50% BB, 50% Bb (100% black).
• Cross C (Bb x Bb): 25% BB, 50% Bb, 25% bb (25% brown).
• Cross D (bb x bb): All offspring bb (100% brown).

Why D is correct:

• Crossing two homozygous recessives (bb x bb) yields 100% bb offspring, ensuring all express the recessive brown trait per Mendel's law of segregation.

Why the others are wrong:

• A: Yields only dominant black (BB) offspring.
• B: Yields only black phenotypes (BB or Bb).
• C: Yields only 25% recessive brown (bb) offspring.

Final answer: D