Mendel's Laws > The Law of Dominance

Law of Dominance states that “When two homozygous individuals with one or more sets of contrasting characters are crossed, the characters that appear in the F₁ hybrid are dominant and those that do not appear in F₁ are recessive characters".

According to the law of dominance:

1. The law of dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the F₁ and the expression of both in the F₂ generation. It also explains the proportion of 3:1 obtained at the F₂.
2. The characters are controlled by discrete units called factors, which are now called alleles.
3. Factors occur in pairs.
4. In a dissimilar pair of factors, one member of the pair is dominant and the other is recessive.
   For example - Tallness in pea plants is a dominant character, while dwarfness is a recessive character.
   
5. In a cross between pure tall and pure dwarf pea plant, the only tall character is expressed in all the individuals of F₁ generation. As a result, tallness is the dominant character in pea plants, while dwarfness is a recessive character.
6. Tallness in F₁ hybrid is determined by genotype Tt, in which the dominant allele 'T' suppresses the recessive allele 't', thereby suppressing its expression in the phenotype.
7. The Law of dominance is significant and true but it is not universally applicable.

The law of dominance states that, out of a pair of allelomorphic characters one is dominant and the other recessive.

1. In a pair of contrasting traits, only one trait is expressed—this is the dominant trait.
2. The trait that remains unexpressed is called recessive.
3. The recessive trait can express itself only when both alleles are recessive (homozygous recessive).