Final answer:
Trans-effects in terms of histone modifications refer to the modifications of histone proteins and DNA that affect chromatin structure and gene expression. These modifications can signal whether a gene should be turned on or off.
Step-by-step explanation:
Trans-effects in terms of histone modifications refer to the modifications of histone proteins and DNA that affect chromatin structure and gene expression. These modifications can signal whether a gene should be turned on or off. For example, histone acetylation tends to unwind nucleosomes and open the underlying DNA for transcription, while methylation can either open or close DNA for transcription depending on the specific lysine or arginine being modified. These modifications affect the accessibility of RNA polymerase and transcription factors to the DNA, ultimately determining whether transcription occurs or not.