Problem:
Question: How is the expression of genes controlled at the chromosomal level?
a) DNA is spontaneously deleted from a chromosome if unneeded.
b) DNA can either be condensed into heterochromatin or unwound into euchromatin.
c) DNA can synthesize extra histones as needed.
d) DNA can be unwound into euchromatin to reduce the level of expression.
e) The expression of DNA can only be controlled at the transcriptional level.
Provide the correct answer and justification for your choice.