Suppose there are two different mutant alleles of the same gene. Sequence analys

Question

Suppose there are two different mutant alleles of the same gene. Sequence analysis shows that both alleles are single nucleotide substitutions, and that different nucleotide positions within the gene are affected in each allele. Phenotypic analysis shows that one allele is a null allele, and the other is dominant negative (antimorphic) Explain what this information reveals about the two mutations. Give a hypothesis for how these two mutant alleles could show such markedly different effects. [10 marks]

Explanation / Answer

please read carefully till the end. The middle paragraph is just to enhance comprehension.

A null Allele is one which has lost it's function. The reason behind this is that the allele is not able to make a functional copy of the protein. Say it changes the amino acid constitution such that the protein no longer binds to its substrate given to altered structure.

On the other hand, the mutation causing the allele to become dominant may be because normally the protein would be produced as inactivated copy, activated by binding of a cofactor or truncation of a part. But a mutation removed the need to be activated, thus causing its expression constitutively.

But in our case the mutation is antimorphic. The reason this kind can become dominant is may be that the protein works as a dimmer. Hence only one unit alone cannot produce function causing it expressed in dominant fashion.

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