1. DNA (Deoxyribonucleic Acid): This is the genetic material that carries the instructions for building and maintaining an organism. DNA is organized into genes, which are segments of DNA that code for specific proteins.

2. Proteins: These play a crucial role in packaging and organizing the DNA, providing structural support and regulating gene expression. The most abundant type of protein in chromosomes is histone.

Together, DNA and proteins form a complex structure called chromatin, which is the building block of chromosomes.