Question

1. Explain what classifies a mutation as “temperature‑sensitive” by comparing phenotype(s) with a wildtype allele.
2. How is this type of phenotype explained by protein behaviour?

1. Would the following types of mutations most likely have: severe effects, mild effects, or no effect on protein function? Briefly explain your answers. Note that there may be more than one correct answer, but you need only to give one sensible answer and explain your reasoning.                                                                                                                                               [6 marks]

1. A nonsense mutation occurring in sequences encoding amino acids near the carboxy terminus of the protein
2. A missense mutation affecting the active site of the protein
3. A frameshift mutation near the 5’ end of the open reading frame

Answer 1

Explain what classifies a mutation as “temperature‑sensitive” by comparing phenotype(s) with a wildtype allele.
The temperature sentivive mutation means, the phenotype is observed only in the permissible or optimal temperature. Suboptimal or higher temperature inhibits the expression of required phenotype. This is the basic logic of temperature mutant. For example, the Himalyan rabbit. It exhibits red eyes and white fur in the colder temperature, and when temperatures rise, it looses its characteristic look.
This is the classical example of temperature mutant. such mutants are regularly used in research to produce gene silencing or gene knowckouts.

How is this type of phenotype explained by protein behaviour?
When the temperature is permissible, the mutant protein is expressed and properly folded. Such proteins function normally and produce the phenotype. But when the temperature is not permissible or higher, the proteins do not fold normally and this results in loss of protein function, resulting in loss of phenotype.

Would the following types of mutations most likely have: severe effects, mild effects, or no effect on protein function? Briefly explain your answers. Note that there may be more than one correct answer, but you need only to give one sensible answer and explain your reasoning.   
A nonsense mutation occurring in sequences encoding amino acids near the carboxy terminus of the protein
   Non sense mutation adds stop codons to the sequence. But the site is carboxy which is the end region of the protein, so the non sense mutation will not have any effect on the normal protein function.
  
A missense mutation affecting the active site of the protein
   Missense mutation, results in addition of different amino acid. Such point mutations in the active site of the protein would have mild effects on the function of protein.
  
A frameshift mutation near the 5’ end of the open reading frame
   Frameshift mutation would mean skipping the first start codon, but the next AUG may be used as start codon. This would result in entire sequence to be read in wrong way and protein formed may not carry the intended function. so effect is severe.