Explain the concept of dominance.

Explanation

Every gene contains the information to express a particular trait.
= In a diploid organism there are two copies of each gene i.e, as a pair of alleles.
= These two alleles need not always be identical as in a heterozygote.
= One of them may be different due to some changes that it has undergone which modifies the information that particular allele contains.
= Let.s take an example of a gene that contains the information for producing an enzyme.
= Now there are two copies of this gene, the two allelic forms.
= Let us assume that the normal allele produces the normal enzyme that is needed for the transformation of a substrate S.
= Theoretically the modified allele could be responsible for production of: (i) the normal/ less efficient enzyme or (ii) a non-functional enzyme or (iii) no enzyme at all.
= In the first case, the modified allele is equivalent to the unmodified allele i.e. it will produce the same phenotype/trait i.e. result in the transformation of substrate S.
= Such equivalent allele pairs are very common.
= But, if the allele produces a non-functional enzyme or no enzyme, the phenotype may be effected.
= The phenotype/trait will only be dependent on the functioning of the unmodified allele.
= The unmodified (functioning) allele, which represents the original phenotype is the dominant allele and the modified allele is generally the recessive allele.
= Hence in the example above the recessive trait is seen due to non-functional enzyme or because no enzyme is produced.