Question

Question 8 [14 marks / 14 minutes]
Design mutations of hypothetical protein-coding genes:
a)Design a null mutation where the site of the mutation is outside the Open Reading Frame (ORF).Explain how your mutation fits the definition of a null mutation. [5 marks]
b)What type of mutagen could generate your null mutation? Explain.[2 marks]
c)Design a mutation that is not a null allele. Explain the consequence of your mutation for thefunction of the protein. [5 marks]
d)What type of mutagen could generate your second mutation? Explain.[2 marks]

Answer 1

A hypothetical protein codin gene can have any of these mutations, like null mutation (loss of function mutation) , gain of function mutations , biochemical mutation (having a lesion of one gene in an enzymatic pathway), restrictive mutation( where the mutation is active only in specific conditions) ,conditional mutation or a lethal mutation.

a. One can completey knock out both alleles of the gene that interacts with this hypothetical protein and whose funtion is dependent on the knockout gene. Knocking the selected gene should not result in lethality. The dependent gene that expresses a particular protein which interacts with hypothetical protein would definitely be not produced, severely affecting the function of hypothetical protein. The mutation is made outside ORF. This kind of strategic knockout can help us to decipher the function of dependent gene as well as hypothetical gene along with necessary controls.

b. Some of the mutagens like UV rays or X rays , extreme temperatures or chemicals like intercalating agents can disrupt the function of a gene completely, leading to behave as if it is a null mutant.

c. If the mutation is not a null allele, it can be a point mutation that severely affects the function of protein. For eg: a single point mutation in Notch receptor (mutation such as L1594P, I681N or R1599P) severly affects the function of Notch receptor in context of T-cells and cause T-acute lymphoblastic leukemia (T-ALL). Similar point mutation within the hypothetical gene could abrogate the function of the gene. Other mutations could be deletions or insertions to change the ORF of the gene.

d. Mutagens mostly cause spontaneous or non specific mutations (at high doses). If one use UV rays to affect thymine for 1st mutant , one could use a deaminating agents (like nitrous acid) or hydroxylating agents (hydroxylamine) or alkylating agents for second mutation to occur.