Which of the following processes involves changes to chromatin structure affecting gene expression?

Histone modification is a crucial process that alters the structure of chromatin, which in turn significantly impacts gene expression. Chromatin is made up of DNA wrapped around proteins called histones. When histones undergo modifications, such as acetylation, methylation, or phosphorylation, this can lead to a more open or closed chromatin structure.

An open chromatin structure allows for easier access for transcription factors and RNA polymerase, facilitating the transcription of certain genes. Conversely, a closed chromatin structure restricts access, thereby inhibiting gene expression. These modifications can be heritable, influencing not just the individual gene expression patterns but also contributing to the overall epigenetic landscape of the organism. Therefore, histone modification directly links chromatin structure to gene regulation and expression, making it the correct answer to the question.

The other processes mentioned, such as DNA replication, RNA splicing, and protein synthesis, do not involve direct changes to chromatin structure. DNA replication is primarily concerned with duplicating the genetic material. RNA splicing involves the processing of RNA after transcription, and protein synthesis translates RNA into proteins, all of which are downstream processes that do not modify the chromatin itself.