What is the name of a small circular DNA molecule that carries accessory genes separate from the bacterial chromosome?

• A. Chromosome
• B. Ribosome
• C. Transposon
• D. Plasmid

Answer: (D)

Plasmids are small circular DNA molecules that exist outside the bacterial chromosome and replicate independently. They carry accessory genes that aren’t essential for everyday survival but can provide advantages, such as antibiotic resistance or special metabolic abilities. Because they have their own origin of replication, plasmids are extrachromosomal, distinct from the main chromosome which contains essential genes. They can be transferred between bacteria through processes like conjugation, helping spread these advantageous traits. This combination of circular structure, independent replication, and nonessential accessory genes matches the description perfectly. Chromosomes are the main, larger genetic material with essential genes; ribosomes are the complexes that translate RNA into protein; transposons are mobile elements that move within genomes and aren’t typically independent circular DNA maintained outside the chromosome.