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Q.
A recessive allele is expressed in
Principles of Inheritance and Variation
Solution:
The factor of an allelic or allelomorphic pair which is unable to express its effect in the presence of its contrasting factor in a heterozygote is called recessive factor or allele, e.g., the allele $'t'$ in hybrid tall pea plant $Tt$. The effect of recessive factor becomes known only when it is present in the pure or homozygous state, e.g., $tt$ in dwarf pea plant.