What is the definition of a chromosome?

A chromosome is defined as a tightly coiled strand of DNA. This structure is essential for the organization and packaging of genetic material within the cell. Chromosomes become highly compacted during cell division, ensuring that DNA is accurately distributed into daughter cells. In humans, for example, most cells contain 46 chromosomes, which house the genetic instructions necessary for the growth, development, and functioning of the organism.

The other options describe various aspects of genetic material but do not capture the complete definition of a chromosome. A double-stranded RNA molecule refers to a different biological entity that is not involved in the structural organization of genetic material as chromosomes are. A hereditary unit consisting of DNA is a broader term that could refer to genes, which are segments of DNA found within chromosomes but do not describe the whole structure. Similarly, a type of RNA that carries genetic codes refers to mRNA, which plays a role in protein synthesis rather than serving as the physical structure that houses genetic information like chromosomes do.