Which organism is characterized by having thousands of origins of replication?

• A. Eukaryotes
• B. Prokaryotes
• C. Viruses
• D. Archaea

Answer: (A)

Multiple origins of replication are needed when genomes are large and organized as linear chromosomes, so replication can proceed in many directions at once and finish within the cell’s S phase. Eukaryotic chromosomes are long and linear, spanning many thousands of base pairs, and they employ thousands of origins scattered along their length. This distribution allows numerous replication forks to operate simultaneously, ensuring the entire genome is copied efficiently.

In contrast, prokaryotes typically have a single, circular chromosome and use one origin of replication to initiate bidirectional copying, which is sufficient for their much smaller genomes. Archaea can have multiple origins as well, but their numbers are not on the scale of thousands. Viruses generally have compact genomes and rely on host machinery, so they do not require thousands of origins.

So, the feature of having thousands of origins of replication is a hallmark of eukaryotic genomes.