Final answer:
The correct order from least to most complex structure of DNA organization in chromosomes is DNA, nucleosome, chromatin, and chromosome.
Step-by-step explanation:
Organization of DNA in Chromosomes
DNA is organized into chromosomes with increasing levels of structural complexity. The correct order from the least to the most complex organization is DNA, nucleosome, chromatin, and finally chromosome. Starting at the most basic level, DNA wraps around histone proteins to form nucleosomes, which resemble beads on a string and contribute to the first level of DNA packing. These nucleosomes are further organized into chromatin, a less condensed form except when the cell is preparing to divide. Ultimately, the most condensed and organized form of DNA packing within the cell is known as the chromosome, which assures proper separation during cell division.