Final answer:
In the 'beads-on-a-string' structure of chromatin, the component not retained is the linker (H1) histone, whereas linker DNA, nucleosome core particles, and core histones are present.
Step-by-step explanation:
The "beads-on-a-string" model of chromatin structure refers to DNA in its most decondensed state. When chromatin is experimentally reverted to this form, certain components are not retained. Specifically, the components that are not retained when this structure is generated are: (a) linker (H1) histones. The linker or H1 histones associate with the DNA as it enters and exits the nucleosome, thereby contributing to the higher-order structure, which is lost in the most decondensed form of chromatin. In contrast, the components that are retained include: (b) linker DNA, (c) nucleosome core particles, and (d) core histones. The nucleosome core particles, composed of core histones around which the DNA is wound, and the linker DNA that connects nucleosomes, remain present in the beads-on-a-string structure.