Satellite DNA, a class of highly repetitive non-coding DNA, is characteristically absent in prokaryotes and plasmids. The correct answer is 2. A, B only.

Option Analysis

Plasmid (A)

Plasmids are small, extrachromosomal DNA molecules typically found in prokaryotes. They lack the complex chromatin structure and tandem repetitive sequences defining satellite DNA, which requires eukaryotic chromosomal organization.

Prokaryotes (B)

Prokaryotic genomes (bacteria and archaea) are compact and gene-dense, with minimal non-coding repetitive DNA. While rare satellite-like repeats exist in some species, satellite DNA as defined—abundant tandem repeats in heterochromatin—is generally absent due to evolutionary pressures for genome streamlining.

Eukaryotes (C)

Eukaryotes feature extensive satellite DNA in centromeres, telomeres, and heterochromatin, aiding chromosome structure and segregation. This option is incorrect as satellite DNA is a hallmark of eukaryotic genomes.

Drosophila (D)

Fruit flies like Drosophila have well-documented satellite DNAs (e.g., 1.672 satellite), comprising significant portions of their genome for functions like chromatin packaging.

Yeast (E)

Yeast (Saccharomyces cerevisiae), a eukaryote, contains ribosomal DNA repeats and other tandem arrays akin to satellite DNA, though less abundant than in higher eukaryotes.​

Satellite DNA absent prokaryotes plasmids is a key NEET biology concept testing repetitive DNA distribution. These tandem non-coding repeats, named for distinct centrifugation bands, dominate eukaryotic heterochromatin but are missing from prokaryotic genomes and plasmids.

Eukaryotic Abundance

In eukaryotes like humans, Drosophila, and yeast, satellite DNA forms blocks at centromeres/telomeres, stabilizing chromosomes. Drosophila boasts prominent satellites (e.g., 359-bp repeats), while yeast has rDNA arrays.

Prokaryotic Absence

Prokaryotes prioritize compact genomes; satellite DNA’s repetitive nature would hinder replication fidelity. Rare prokaryotic repeats exist but lack eukaryotic-scale tandem arrays.

Plasmid Exclusion

Plasmids, prokaryote-associated, carry functional genes (e.g., resistance) without heterochromatic repeats like satellite DNA.​

This distinction highlights genome evolution: eukaryotes tolerate “junk” DNA for structure; prokaryotes do not.​