Final answer:
A gene with 4 exons has 3 introns. Introns separate the exons, except for the first and last exon, which do not require an intron on one side. Thus, the answer is three introns. The correct option is c).
Step-by-step explanation:
The question is asking how many more introns are present on a gene that consists of 4 exons. In eukaryotic genes, exons are the coding sequences which are separated by non-coding sequences called introns. The general arrangement is that each exon is flanked by introns, except for the first and last exon.
For a gene with 4 exons, there are exons at the beginning and end of the gene sequence that do not require an intron on one side. Therefore, in between each of these exons, there would be an intron.
This would mean that there are 3 introns needed to separate these exons (Intron-1 between Exon-1 and Exon-2, Intron-2 between Exon-2 and Exon-3, and Intron-3 between Exon-3 and Exon-4).
The correct answer to the question is therefore c. Three, which is how many more introns are present on a gene that consists of 4 exons.