1 How to fill it
- One parent's two letters <b>across the top</b>.
- The other parent's two <b>down the side</b>.
- Each box takes the letter above it and the letter beside it.
- Four boxes. Four combinations. Nothing else.
"One from each, every box."
2 Two ratios, not one
- <b>Genotype ratio</b> — the letters. Tt × Tt gives <b>1 TT : 2 Tt : 1 tt</b>.
- <b>Phenotype ratio</b> — what you see. The same cross gives <b>3 : 1</b>.
- They differ because <b>TT and Tt look the same</b>.
"Which ratio is being asked for?"
3 What it says
- A <b>chance</b>, for <b>each</b> offspring, <b>separately</b>.
- 3 : 1 means each one has a 3 in 4 chance.
- With 400 seeds the count lands close.
- With 4 children it very often does not.
"Each one is a fresh throw."
4 What it does NOT say
- Not <b>three of your four children</b>.
- Not <b>dominant means common</b> — extra fingers is dominant and rare.
- Not <b>Tt is halfway</b> between TT and tt.
- Not <b>the next one is due</b>.
"The dice do not remember."