USA Biology Olympiad (USABO) Practice Exam

What essential components does a linear chromosome typically contain?

1. One centromere and multiple origins of transcription

2. Two telomeres and many origins of replication

3. A single telomere and a centromere

4. Various genes and two centromeres

The correct answer is: Two telomeres and many origins of replication

A linear chromosome typically contains two telomeres, which are protective caps located at both ends of the chromosome. These telomeres play a crucial role in maintaining chromosome stability and protecting the genetic data during cell division. Additionally, linear chromosomes have multiple origins of replication, which are necessary for the replication process to begin at various points along the chromosome, ensuring that the entire DNA is replicated efficiently and accurately during the S phase of the cell cycle. This setup allows for a faster replication process compared to a single origin, which would result in a longer time needed for chromosome duplication. While other options contain components that are relevant to chromosomes, they do not accurately describe the typical structure of a linear chromosome. For instance, having a single telomere and a centromere does not reflect the actual structure since each linear chromosome must have a telomere at both ends, and a chromosome cannot possess two centromeres as that would define it as an abnormal structure leading to complications in segregation during cell division. Hence, the presence of two telomeres along with multiple origins of replication is essential for the proper function and integrity of linear chromosomes.