Histone modifications are chemical changes to the proteins called histones that help package and organize DNA in the cell nucleus. These modifications can include the addition or removal of chemical groups, such as methyl or acetyl groups, which can influence how tightly or loosely DNA is wrapped around the histones. This affects gene expression, determining whether specific genes are turned on or off. Different types of histone modifications can work together to create a complex code that regulates various cellular processes. This code plays a crucial role in cell differentiation, development, and responses to environmental signals, ultimately influencing an organism's traits and functions.