1. Tardigrade
  2. Question
  3. Biology
  4. The modified allele should be responsible for production of: I. the normal/less efficient enzyme II. A non–functional enzyme III. No enzyme at all

Q. The modified allele should be responsible for production of:
I. the normal/less efficient enzyme
II. A non–functional enzyme
III. No enzyme at all

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Solution:

Every gene contains information to express a particular trait. Diploid organisms have two copies of each gene, they are called alleles. These two alleles may be identical or non-identical. One of them may be different due to mutation (sudden change in genotype) that it has undergone which modifies the information that particular allele contains. Suppose that the normal allele produces the normal enzyme that is needed for the transformation of a substrate S. Theoretically, the modified or mutated allele could be responsible for the production of:
(i) The normal/less efficient enzyme, or
(ii) A non-functional enzyme, or
(iii) No enzyme at all
In case (i), the modified allele is equivalent to the unmodified allele, i.e., it will produce the same phenotype/trait as in case of silent mutation. But, if the allele produces a non-functional enzyme or no enzyme (case (ii) and (iii)), the phenotype may be affected. The unmodified (functioning) allele, which represents the original phenotype is the dominant allele/wild type and the modified allele is generally the recessive allele/ mutant type. Hence, the recessive trait is due to non-functional enzyme or because no enzyme is produced if the mutated allele forms an altered but functional product, it behaves as incompletely or co-dominant allele. Let us take the example of tallness. Plant height depends on the amount of particular plant hormone. The amount of the plant hormone made will depend on the efficiency of the process for making it. Consider now an enzyme that is important for this process. If this enzyme works efficiently, a lot of hormones will be made, and the plant will be tall. If the gene for enzyme has an alternation that makes the enzyme non-functional or no enzyme at all, the amount of hormone will be less and the plant will be dwarf.