Describe Mendel's dihybrid cross between pea plants with round yellow seeds and wrinkled green seeds. What does it show?

1. 1 · Define in one line. A dihybrid cross follows the inheritance of two pairs of contrasting traits together.
2. 2 · Parents and F1. RRYY × rryy → all RrYy, round yellow; round and yellow are dominant.
3. 3 · F1 gametes. RY, Ry, rY and ry, in equal numbers.
4. 4 · Draw the 4 × 4 checkerboard. [16-box checkerboard with the four gametes on both sides]
5. 5 · F2 result. 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green.
6. 6 · Conclusion. New combinations appear, so the two traits are inherited independently; each trait alone still gives 3 : 1.
7. 7 · Link to daily life. Breeders combine useful traits from two varieties into one new crop.
8. 8 · Close in one line. Thus genes for different traits are passed on separately.

Scoring tip: Write the four F1 gametes before drawing the grid; most errors come from wrong gametes.