Confirmation of Mendels First Law - With these observations, Mendel could form a hypothesis about segregation. To test this hypothesis, Mendel selfed the F₂ plants.

If his law was correct he could predict what the results would be. And indeed, the results occurred as he expected.

From these results we can now confirm the genotype of the F2 individuals. Thus the F₂ is genotypically 4 Dd : 2 Dd : 4 dd.

This data was also available from the Punnett square using the gametes from the F₁ individual.

So although the phenotypic ratio is 3: 1 the genotypic ratio is 1:2:1.