Based on homology, a protein, CG2024, functions as a homotetramer. The function of each unit within the tetramer is essential for its catalytic activity. CG2024 protein has three domains. Domain ‘a’ is essential for tetramerization, domain ‘b’ is essential for catalytic activity and domain ‘c’ does not contribute to CG2024 function at all. Three mutations, a*, b* and c* in the ‘a’, ‘b’ and ‘c’ domains of CG2024, respectively, have been identified. The a* and b* disrupt the function of their respective domains.

Based on this information, which one of the following options correctly describes the nature of mutations a*, b* and c* (in the same order)?

Correct option is B

EXPLANATION-

CG2024 Protein Context: CG2024 is a homotetramer (four identical subunits). Domain 'a' is essential for tetramerization, domain  'b' for catalytic activity, and domain  'c' has no role . Mutations  $$a^*, b^*, \text{and} \ c^*$$ affect these domains, with $$a^*, b^*$$disrupting their respective functions.

Mutation $$a^*$$ (affects domain a)

A tetramer needs all four subunits to tetramerize. If even one subunit has $$a^*$$ ,the tetramer may fail to form (since only $$(0.5)^4 = 6.25\%$$. of tetramers will have all wild-type subunits).
This disrupts function in the heterozygote, making $$a^*$$ dominant..

Mutation $$b^*$$ (affect domain b)

Domain b is essential for catalytic activity. In a heterozygote $$(B b^*), 93.75\%$$ of tetramers will have at least one $$b^*$$ subunit.

if one  $$b^*$$ subunit disables the tetramer’s catalytic activity (since all subunits must cooperate), the heterozygote shows a mutant phenotype, making $$b^*$$ , dominant.

Mutation $$c^*$$ (affect domain c)

Domain c has no function, so $$c^*$$ doesn’t affect the protein’s activity, even in a homozygote   ( $$c^*c^*$$).

This mutation has no phenotypic effect, but in genetics, a mutation with no effect is often classified as recessive (since it doesn’t alter the wild-type phenotype in a heterozygote).

Amorphic mutations cause a complete loss of function and are typically recessive. $$c^*$$could be amorphic (no function).

So, the correct option is (b) - Dominant, dominant , amorphic.

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