Chromosomes are the structures that contain genetic information in the form of DNA. They are found within the nucleus of cells and play a crucial role in the transmission of genetic material from one generation to the next. The composition of chromosomes is complex and involves various components.

DNA:
- DNA, or deoxyribonucleic acid, is the primary component of chromosomes. It carries the genetic instructions necessary for the development, functioning, and reproduction of all known living organisms. DNA is a long, double-stranded molecule made up of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base. The sequence of these nitrogenous bases determines the genetic code.

Histones:
- Histones are proteins that play a structural role in chromosomes. They help in the packaging of DNA into a compact and organized structure called chromatin. Histones act as spools around which DNA is wound, forming nucleosomes. There are five major types of histones: H1, H2A, H2B, H3, and H4. These proteins provide stability to chromosomes and regulate gene expression.

Non-Histones:
- Non-histone proteins are another component of chromosomes. They include various proteins involved in DNA replication, repair, recombination, and transcription. Non-histone proteins participate in the regulation of gene expression and the maintenance of chromosome structure. Examples of non-histone proteins include topoisomerases, kinases, and transcription factors.

RNA:
- RNA, or ribonucleic acid, is also present in chromosomes. RNA molecules are produced through a process called transcription, where DNA is used as a template to synthesize complementary RNA strands. Different types of RNA are involved in various cellular processes, such as protein synthesis (messenger RNA or mRNA), regulation of gene expression (microRNA or miRNA), and modification of histones (small interfering RNA or siRNA).

In summary, chromosomes are composed of DNA, RNA, histones, and non-histones. DNA is the main component, carrying the genetic information, while histones provide structural support and help in organizing DNA. Non-histone proteins are involved in various cellular processes, and RNA molecules play important roles in gene expression and other functions.