Question

1. In a particular gene in mice, a single base pair change from GC to an AT at the 5’ end of the first intron causes a longer transcript to be made as well as a non-functional gene product. When such a mutation is present in both copies of this gene in a mouse, the mouse shows a mutant phenotype. Propose a molecularly based explanation for how such a single base change at the start of an intron could specifically result in a longer transcript and a non-functional gene product. Give some details here – this is not a one or two word answer. (5 points)

Answer 1

Ans:- The single Mutation can cause the deletrious or lethal effect depending on the context where the Mutation have happened.In this case mutation at start of intron convert GC to AT. If you look at intron the it's start sequence GC is called 5' splice site. This 5' splice site is recognised by splicing machinery and it defines exon intron boundary. When 5' splice site is mutated to AT, the splicing machinery can't recognised it and unable to perform the splicing of intron. Due to this retention of intron the mRNA transcript produced is longer than produced in wild type counterpart. Once, inside the cell these longer version of mutant mRNA translated into a longer protein. So, it can happen that the amino acid sequence will be different than wild type. Further, these mutated protein may be unable to fold in proper 3D structure that is required for its catalysis. Finally, these mutated protein will be unable to carry out its designated function that results in mutant phenotype.

Dear student if you find the answer convincing please do give the feedback.