Explain Mendel's monohybrid cross with a checkerboard.

1. 1 · Define. A monohybrid cross is a cross between parents that differ in one pair of contrasting characters.
2. 2 · Parents and F₁.
   • P: pure tall (TT) × pure dwarf (tt).
   • Gametes: T and t.
   • F₁: all Tt, tall.
3. 3 · Selfing and gametes. F₁ Tt × Tt; each plant gives T and t gametes.
4. 4 · Draw the checkerboard. [Punnett square: T and t across the top; T and t down the side; TT, Tt, Tt, tt with tall or dwarf written in each box]
5. 5 · Results.
   • Phenotypic ratio: 3 tall : 1 dwarf.
   • Genotypic ratio: 1 TT : 2 Tt : 1 tt.
6. 6 · Laws. Law of dominance (all F₁ tall) and law of segregation (pure gametes).
7. 7 · Link to daily life. Breeders used these rules to develop short, strong-stemmed rice and wheat.
8. 8 · Close. So the dwarf trait was hidden in the F₁, not lost, and came back in the F₂.

Scoring tip: Box the ratios under the checkerboard. Write capital and small letters clearly (T and t).