Question

Q5. Closer examination of the two alleles of the human CDC25B gene reveals no changes in nucleotide sequence in the transcriptional unit. This observation indicates that the difference in nucleotide sequence between the two alleles must not occur within the transcriptional unit. Provide two possibilities where nucleotide changes could occur on the chromosome in the “_” allele that prevents production of CDC25B mRNA and explain why. (4 marks)

Answer 1

5. Mutations can occur in both coding and noncoding regions of a gene.
Mutations that occur in the coding region are qualitative i.e. they affect (increase/decrease) the activity of the gene product.
Mutations that occur in the noncoding region are quantitative i.e. they affect the amount of the gene product produced.
These noncoding regions include a promoter, silencer, operator, and enhancer.

1. Mutations in the promoter region result in the inability of RNA polymerase to bind to the target gene locus resulting in transcriptional repression.
2. Mutations in the silencer region result in the inability of repressor proteins to bind to it. This leads to the enhanced recruitment of RNA polymerase to the target gene locus resulting in transcriptional activation.

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