Final answer:
An unreplicated chromosome is composed of a single DNA double-helix. This molecule of DNA is highly coiled and organized with proteins into a condensed structure. Each strand of the helix serves as a template for the creation of a new complementary strand during the replication process.
Step-by-step explanation:
An unreplicated chromosome consists of a single DNA double-helix. Before replication, each chromosome is one long continuous molecule of DNA that is highly coiled and condensed. During replication, each of the original DNA strands, or parental strands, acts as a template for the creation of new complementary strands. This results in two identical DNA double-helices known as sister chromatids, which are connected at a region called the centromere, giving the replicated chromosome its characteristic X-shape.
In eukaryotic cells, a chromosome before DNA replication is composed of a single DNA molecule that is packaged into nucleosomes and further organized into distinct regions that can be visualized by staining techniques. The chromosomes undergo further coiling during cell division processes like mitosis and meiosis to facilitate their movement within the cell. It's only after DNA replication that the singular DNA double-helix becomes duplicate sister chromatids in the structure of a chromosome.