Final answer:
The statement that introns are found only in nuclear genes is false; introns are characteristic of eukaryotic nuclear genes but can also be present in prokaryotic and mitochondrial genes. They play roles in gene regulation and are critical for proper gene expression and protein synthesis.
Step-by-step explanation:
The statement 'Introns are found only in nuclear genes' is false. While it is true that introns are a characteristic of nuclear eukaryotic genes, where they are spliced out of pre-mRNA before it is translated into proteins, they are also present, though rare, in some prokaryotic and mitochondrial DNA.
Introns are significant because they can play roles in gene expression regulation, and their removal through the process of splicing is critical for the production of functional proteins. If splicing is not carried out correctly, it can result in a nonfunctional protein, as the sequence of the rejoined exons would be shifted.