Final answer:
Eukaryotic chromosomes fit inside the nucleus by packaging DNA into chromatin fibers, where DNA is coiled around histone proteins significantly reducing its effective length.
Step-by-step explanation:
Eukaryotic chromosomes, which are linear structures within the nucleus made up of DNA, can be thousands of times longer than a typical cell. To fit inside a eukaryotic nucleus, DNA must compactly package itself. When not dividing, DNA is not tightly wound but rather exists as chromatin, which are unwound protein-DNA complexes that resemble a jumbled bunch of threads. Chromatin fibers are coiled and folded into various levels of higher-order structures, leading to a significant reduction in the effective length of the DNA strands, enabling them to fit within the confines of a nucleus. The process of DNA packaging is crucial for chromosome organization and function, and it involves wrapping the DNA around histone proteins to form a structure known as the nucleosome.