Final answer:
Introns are more frequent in higher eukaryotes and less frequent in lower eukaryotes.
Step-by-step explanation:
Introns, which are the noncoding portions of a gene, make up about 95% of human nuclear DNA and are rare in prokaryotic and mitochondrial DNA. The role of introns in gene regulation is not fully understood, but they may affect gene expression speed or be remnants from evolution.
Spliceosomal introns, common in higher eukaryotes, are excised from pre-mRNA by a complex called a spliceosome, whereas Group I and Group II self-splicing introns are found more in lower eukaryotes and in specific cases such as bacterial, mitochondrial, and chloroplast genes.