The Square, the Ratio, and the Test

You'll learnhow allele segregation produces predictable offspring ratios, modeled by a Punnett square.

Mendel discovered that inheritance is arithmetic: two alleles separate into gametes, the gametes combine at random, and the ratios follow. Watch the square do the multiplying, then meet the chi-square test that decides whether a ratio you predicted survives the data you counted. Twelve short steps; press Next for each one.

AP BIOLOGY · 12 STEPS · 6 QUICK CHECKS · Aa × Aa → 3:1 · AaBb × AaBb → 9:3:3:1 · SMALL p REJECTS THE NULL · v6

Aa × Aa → 3:1 · the test cross · χ² decides when a miss is real

Before you start

What you're looking at

One homologous pair at a single locus carrying two alleles, A (tall) and a (dwarf): genotype Aa, phenotype tall.

The question

How do two alleles in a parent turn into predictable proportions of offspring?

Step 1 / 12