Final answer:
The correct order from least to most complex organization of genetic material is DNA, nucleosome, chromatin, chromosome.
Step-by-step explanation:
The correct order of structures from least to most complex is as follows: DNA, nucleosome, chromatin, chromosome. DNA is the basic molecule of heredity, consisting of a long chain of nucleotides. Nucleosomes are the basic unit of DNA packaging in eukaryotic cells, composed of a segment of DNA wound around a core of histone proteins. Chromatin is a complex of DNA and protein, mainly histones, that is found inside the nuclei of eukaryotic cells and helps to compact DNA into a smaller volume to fit within the nucleus. Finally, chromosomes are long DNA molecules containing genetic material of the organism, which are further organized and condensed chromatin.