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The allele which is unable to express its effect in the presence of another is called
A. Codominance
B. Supplementary
C. Complementary
D. Recessive

Last updated date: 20th Jun 2024
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Hint: The genes which code for a contrasting pair of traits are known as alleles. Thus, alleles are slightly different forms of the same gene. Moreover, the term allele is used with reference to the other allele.

Complete answer:Codominance –
When both the alleles are expressed equally in the Filial 1 generation then it is termed as Codominance. This phenomenon was first observed in the hair color of the cattle. In Codominance, there is no mixing of the effect of the alleles. Due to this reason, the hybrid offspring resemble both parents.
Example – Human blood group AB. People with blood group AB produce sugars for both antigens A and B.
Supplementary genes: When both the genes contribute to a single characteristic in such a way that one gene can mask the effect of another gene then it is termed as Supplementary genes. They can also be considered as the genes in which one gene produces a certain characteristic and the second gene only supplements it, for example: Grain color in maize is governed by two dominant genes.
Complementary genes: they were first observed by Bateson and Punnett in sweet pea. When both the genes are present on separate loci and interact together to produce the dominant characteristic and if present alone then neither of them can express itself, then it is termed as complementary genes.Example: flower color in Lathyrus odoratus.
Recessive allele: when an allele is unable to express itself in the presence of its own other form, then it is termed as recessive gene. The dominant counterpart of it is known as the dominant gene. Example: the height of plants is governed by two alleles, T for tallness, and t for dwarfness. A plant can be dwarf only when the genotype is tt. Any other type of genotype like TT or Tt produces tall plants only.
Thus, based on the above information we can conclude that the allele which is unable to express its effect in the presence of another is called the recessive allele.
Hence, the correct answer is option (D).

Note:Alleles should not be confused with the genes. The genes are the characteristics that are passed down from the parents to the offspring, unchanged, through the gametes, over successive generations. Mendel called genes as factors. Therefore, the genes are the functional unit of inheritance. They contain the required information to express a certain trait in any organism.