Dominant allele expressed in both homozygous and heterozygous condition.

or Principle of Dominance

In heterozygous individuals or hybrids a character is represented by two contrasting factors called alleles or allelomorphs. Out of the two contrasting alleles. Only one is able to express its effect in the individual. It is called dominant factor or dominant allele.

The other which does not show its effect in the heterozygous individual is called recessive factor or recessive allele. The cross between the pure tall and pure dwarf gives all progeny $\left(F_{1}\right)$ tall.

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The character shown by $F_{1}$ called dominant character