If the shape of radish is under the control of one gene, for example A than we can say:
AA is dominant homozygous genotype-round radish phenotype,
aa is recessive homozygous genotype-long radish phenotype
If we cross round and long radish:
P: AA  x  aa
F1: Aa  Aa  Aa  Aa Â
Aa is heterozygous genotype-oval phenotype
If we than cross the F1:
Aa  x  Aa
F2: AA  Aa  Aa  aa
This means that the ratio between the phenotypes woul be  1:2:1 (round:oval:long).