**Question:** Highly repetitive DNA is seen in -

**Core Concept:** Repetitive DNA sequences are stretches of DNA that contain the same nucleotide sequence multiple times. They can be classified into two main categories: simple and complex repetitive sequences. Simple repetitive sequences are short (typically 100 bp) and include satellites and palindromes.

**Why the Correct Answer is Right:** Complex repetitive DNA sequences are characterized by their length, which is much longer than simple repetitive sequences. They are found in higher eukaryotic organisms, providing structural stability to chromosomes and contributing to genome size. The repetitive sequences are composed of tandemly arranged units, ranging from 150 bp to several thousand bp in length.

**Why Each Wrong Option is Incorrect:**

A. Simple repetitive DNA sequences are shorter and not specific to any particular organism or tissue type, making them less relevant for this question.
B. Simple repetitive DNA sequences are not long enough to be considered complex repetitive DNA sequences, making them an incorrect choice.
C. Although repetitive DNA sequences are found in all eukaryotic genomes, complex repetitive DNA sequences are more specific to higher eukaryotes, making option C incorrect.
D. Complex repetitive DNA sequences are not found exclusively in prokaryotic organisms, making option D an incorrect choice.

**Clinical Pearl:** The presence of complex repetitive DNA sequences in higher eukaryotes contributes to genomic variation and structural complexity. Genomic variation is essential for speciation, evolution, and adaptation to environmental changes. Additionally, the repetitive DNA sequences play a role in genomic imprinting, a phenomenon where an allele's expression is subject to parent-of-origin-dependent regulation. This can lead to epigenetic differences between individuals and can result in diverse clinical manifestations.

**Correct Answer:** C. Complex repetitive DNA sequences are found in higher eukaryotes.