Introns are the non-coding nucleotide sequences that are removed by a process called RNA splicing (ribonucleic acid). The spliceosomes remove the introns from the messenger ribonucleic acid (mRNA). The process of RNA splicing follows the transcription process and is called post-transcriptional modification.
Mutation is the sudden change that results in change of nucleotide sequence. The insertion of nucleotide into the gene causes insertional mutation. Thus, the sequence of produced protein varies.
In the given condition, the addition of 4 base pair length nucleotide sequence into the intron has no effect on gene expression. This is because intron is a non-coding sequence.
Hence, the correct option is a.
Exons are the coding nucleotide sequences that are joined to form a gene after the process of RNA splicing (ribonucleic acid). The insertion of nucleotides into the exons effects the expression of gene. Hence, the option (b) is not correct.
The segment of nucleic acid that regulates the expression of a gene is called regulatory sequence. The insertion of nucleotides may result in non-functioning of the regulatory sequence. Hence, the option (c) is not correct.
The insertion of nucleotides into the intron has no effect on gene expression, while nucleotide insertion into the exon effects the gene expression. Hence, the option (d) is not correct.