The law of dominance states that when parents with pure, contrasting traits are crossed together, only one form of the trait appears in the next generation.
The trait which appears in the next generation is known as a dominant trait.
The trait that do not express is called a recessive trait.
It expresses only in a homozygous condition.
Example:
Consider two-parent pea plants.
One with green seeds (GG) and the other with yellow seeds (gg).
When these two pea plants are crossed, the next generation is produced.
The next-generation plants have green seeds (Gg) only.