7 pairs
Explanation
Mendel chose 7 pairs of contrasting characters from pea plants for his experiments. These pairs of characters were:
- Seed color (green vs. yellow)
- Seed shape (round vs. wrinkled)
- Pod color (green vs. yellow)
- Pod shape (inflated vs. constricted)
- Flower color (purple vs. white)
- Plant height (tall vs. dwarf)
- Flower position (axial vs. terminal)