Describe incomplete dominance.  

When experiments on peas were repeated using other traits in other plants it was found that sometimes the $F_{1}$ had a phenotype that did not resemble either of the two parents and was in between the two.

The inheritance of flower colour in the dog flower (Snapdragon or Antirrhinum sp.) is a good example to understand incomplete dominance.

In a cross between true - breeding red flowered [$RR$] and true - breeding white flowered plants ( $rr$) the $F_{1}[R r]$ was pink.

When the $\mathrm{F}_{1}$ was self pollinated the $\mathrm{F}_{2}$ resulted in the following ratio $1$ [ $RR $] Red : $2[\mathrm{Rr}]$ Pink : $1[\mathrm{rr}]$ White.

Here the genotype ratios were exactly as we would expect in any mendelian monohybrid cross, but the phenotype ratio had changed from the $3: 1$ dominant : recessive ratio.

$'R'$ was not completely dominant over $r$ and this made it possible to distinguish $\mathrm{Rr}$ as pink from $RR$ [red] and $rr$ [white].