For any given gene there exists two or more variant forms known as the alleles.
The allele can either be dominant or recessive.
A dominant allele is the one which determines the phenotype in both heterozygous and homozygous condition whereas the recessive phenotype is only shown in case of a homozygous condition.
Since the trait of wrinkled seeds is determined by a recessive allele, it is necessary for the allele r to be present in homozygous condition
