What is meant by the "beads on a string" model of chromatin?
(a)the beads are the nucleosomes, and the string is the linker dna.
(b)-the beads are ribosomes, and the string is the mrna that has been transcribed from active chromatin.
(c)-the beads are molecules of dna polymerase that attach to the dna string.
(d)-the beads are the histones, and the string is the transcriptionally active dna loops.
(e)- the beads are the heterochromatic regions that are tightly compacted, and the strings are euchromatic regions that are being actively transcribed.

The answer to your question is: letter A

Explanation:

Beads on a string is a nucleosome (beads) with a string wrap around it (DNA).

(a)The beads are the nucleosomes, and the string is the linker DNA.  This option is describing perfectly what the expression "beads- on a string means".

(b)-The beads are ribosomes, and the string is the mRNA that has been transcribed from active chromatin.  Ribosomes are very useful organele in the traduction process but are not part of the expresion "beads on a string".

(c)-The beads are molecules of DNA polymerase that attach to the DNA string.  THis option is wrong, beads are the nucleosomes.

(d)-The beads are the histones, and the string is the transcriptionally active DNA loops.  Beads on a string do not consider that DNA is being unde rtranscription.

(e)- The beads are the heterochromatic regions that are tightly compacted, and the strings are euchromatic regions that are being actively transcribed.

This option is incorrect.