Question

Histone modification: is fixed; once a histone is modified, it stays that way and the genes with which it is associated are turned on or off permanently. is random and independent of the environment or cell type. is fixed, but this has no effect on whether genes are expressed. can change over time in response to environmental cues, allowing genes to be turned on or off as needed. can change over time in response to environmental cues, but this has no effect on gene expression.

Answer 1

Answer:

The correct answer is ''can change over time in response to environmental cues, allowing genes to be turned on or off as needed.''

Explanation:

Histones are a family of proteins involved in compacting DNA into structural units called nucleosomes. Histone modifications occur in response to environmental conditions, and modulate the structure of chromatin, that is, they alter the structure of nucleosomes and therefore chromatin, and thus activate the transcription process, in which the chromatin is in the euchromatin state (loose conformation, in which the DNA information can be read), or "off" state, in which the chromatin adopts the heterochromatin conformation (compact conformation, which prevents reading), respectively. These post-translational modifications are mainly acetylation, methylation, phosphorylation, although there are many others. These make up the “histone code” that can change the expression pattern of some genes by modifying the chromatin structure, activating or silencing these genes.