If an organism expresses a recessive phenotype it must be carrying two recessive alleles. The recessive trait is only expressed if there is no dominant allele. As an example, let’s say that flower color is determined by one gene.
There are red and blue flowers.
Red is dominant
Blue is recessive
You have the following for genotypes
FF, Ff, fF, ff
Any genotype with a big F has the dominant red allele. The phenotype will be a red flower. If there is no big F then the blue allele will be expressed.
Genotype
|
Phenotype
|
FF
|
Red Flowers
|
Ff
|
Red Flowers
|
fF
|
Red Flowers
|
ff
|
Blue Flowers
|
The ff genotype will display the recessive gene because there is no big F to be dominant.