In incomplete dominance, both the genes express themselves equally in the heterozygous condition. Therefore, three different kinds of phenotypes would be seen in the F
2 generation in a monohybrid cross.
Example: Colour inheritance in snapdragon.
Red flower: RR; White flower: rr
F1 generation: RR * rr
↓
Rr
F2 generation: Rr * Rr
↓
RR Rr Rr rr
Three phenotypes are seen i.e. Red (RR), pink (Rr) and white (rr).
According to the law of dominance, the phenotype of Rr should be red since R is dominant over r. But Snapdragon does not follow Mendelian inheritance. R is not able to completely express itself over r. This results in a third phenotype (here, pink).
Therefore, three phenotypes are seen in F2 generation in a monohybrid cross.