World 1 · Mendel Basics · 6 minReading ratios
Genotype vs phenotype ratios
Teaching this? Open projector mode
A single Punnett square gives two different ratios:
- Genotype ratio — how the allele pairs are distributed (
1:2:1). - Phenotype ratio — how the visible traits are distributed (
3:1under complete dominance).
These are only expected ratios. Real litters are small, so a Cc × Cc pairing might give 4 cobalt pups by chance. The more offspring you breed, the closer the tally gets to 3:1 — the law of large numbers.
Check yourself
The genotype ratio of a Cc × Cc cross is:
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